Please I am very frustrated with infiltrator and thinking I am doing it wrong. Help.

With the new NS SMG weapon, you do not need to burst fire at all if you have the advanced lasers.
Not that I ever burst fire on any of my SMGs.... It's the easiest to headshot with at a distance.
Also, do aim at the head. If you cannot, try practicing hitting their upper body until you can reliably do that.
You can attack head on, if you can aim at the head.. Usually, you will win. If not, then you'll lose more often than win.
When hitting from the back or whatever, do not stop shooting until the target is really dead.
Like with the auto scouts, I always stopped thinking they will die (since all other guns would have killed them with those many bullets) with all those bullets, but they didn't and eventually killed me since I stopped. Just don't do that.

You can ADS, I do with the 1st gen SMG. You can do that with the new one too. It's great at both. Actually, the best SMG for ADS and hip fire.
I wouldn't bind my melee with RMB, hitting T or whatever the default key is, is pretty easy to do.
Just do what you want on your key bindings.

1st gen SMG.(VS, and I use ADS)
I use, extended Mag, 1x reflex or NV, and suppressor. Since VS has 25 rounds in their SMG, I find that really low.>.
2nd gen SMG.(VS, and I never use ADS)
I use, max Laser, same scopes as above, and suppressor.
NS SMG(I hip fire mostly, but far range, I ADS- really far range)
I use, Max Laser, higher magnification attachment(since you do not ever need to ADS at 1-50m), and suppressor

I'm too cheap to get more SMGs with another faction. So I don't know much about the others..

I don't play INF so I'm not sure what advice I could give you other than to hang in there and work through the frustration. Eventually you will adapt to the game and your bad internet connection. Trust me, I have been there. I started out gaming with a bad (200+ ping usually) internet connection myself.

Do not engage head on, even if you get the first shots off, you can still lose quickly because of the low HP on the class. The trick is to approach people from the sides and the back. Make sure you have a silencer on your SMG to help keep you hidden after you kill the first person. I use the Blitz with a silencer, but any SMG will work fine since they are all relatively balanced. If you learn to outsmart your enemies you can do some serious damage...

Along with the many good suggestions here, get yourself concussion grenades particularly useful when you are taking on a group of enemies with SMG.

Errr, Conc are Heavy Assault grenades.

IMO, the Blitz is much more forgiving, don't know if this comment helps....

Be patient, take a break if it started feels like a chore.

I will try to get better..it will take awhile i guess.

Doh i meant emp

Here are a few things I've learned, because believe me, when I first tried out this class, it was a disaster.

So if you're like me, you find yourself in situations where you're running in your cloak and a heavy is running at you. You could uncloak and open fire, but odds are, the heavy will be able to win. He will win for four reasons- one, he has more health. Two, he has his shields that will turn your bullets into candy. Three, his weapons might be more powerful depending on the situation. Four, uncloaking takes about a second or two, but the moment you press that key, you become visible, so you're basically standing helpless for an entire second. So all in all, you might think you're doomed here. Well... maybe not.

Utilize cover with everything you've got! Buildings, rocks, trees, these are your allies. Use your cloak to get to cover and stay behind cover to recharge it. Open areas are an infiltrator's worst nightmare because your cloak only lasts 10 seconds. If you're caught in the open without your cloak, you'll be cut to pieces. If you're being harassed or chased, use every object in the vicinity to turn it around on your opponent. Go into cloak and start ducking in and out of various areas of cover until you end up behind your foe... then open fire and you should win.

Speaking of getting behind your foe, ambush is the infiltrator's best friend. When the infiltrator update comes out, the decoy grenades will make an excellent ambush tool. For now, use your cloak to access areas that enemies wouldn't expect you to be, and use the cloak to make sure nobody sees you spring your attack. Finally, depending on your tools (that is, if you don't have a suppressor) cloak and get out of the vicinity. The cloak does remove a spot on your head and from the minimap, so after firing your unsuppressed weapon, cloak.

Remember that your cloak makes a ridiculously loud noise. Adjust accordingly. While we're on that subject, also remember that your cloak is not perfect even though it recently got better in the last update.

Upgrade your sensor dart as soon as possible. Once you get it up to the second to last tier, you should have a very potent tool (the last tier is ridiculously expensive, so you can hold off on it) to make sure nobody gets the jump on you. Bouncing betties are fantastic to cover an area that you couldn't ordinarily, as either an enemy will step on it and die, or they will survive but you'll know they're there and probably injured. On top of stairs, around corners, and in those lifts make excellent places because of the profile of the mines. I'd recommend these as your second priority. Get your nanoweave armor upgraded. That'll help out a bit in augmenting to your low shields. It'll help you survive a bullet or two. I don't recommend nano-armor cloaking because its cons outweigh its pros. Stick to hunter cloaking and upgrade that when you get the certs.

Don't be afraid to get out of there. If you find yourself outmatched, do what I said above and utilize your cover to make your escape.

KEEP MOVING WHILE SHOOTING. Strafing is an advantage with an smg because this weapon doesn't require aiming down sights, while something like an LMG does, so you can move at normal speed. Jump around, move, don't stand still and hope to overpower your foe. Even if you approach from behind, if the heavy pops his shield, he'll be able to turn around and put a slug in your mug. Speaking of movement, that scenario I started off with? Well, if the heavy still doesn't see you and you can't run or duck behind cover, move to one side of him before uncloaking and opening fire. The time it will take for him or her to aim at you accurately will compensate for the time it will take you to open fire, maybe even surpass it, so you'll get a fighting chance.

Finally, get yourself a decent side-arm. The cyclone is an awesome weapon and is, IMO, the best smg in the game (or at least my favorite). However, it only has 25 rounds. If you're used to the hundred or so rounds in an LMG, this'll be an issue. If you find yourself out of rounds but your enemy is still alive and is out of melee distance, use your sidearm as it's faster to switch to that than reloading. The NC have a good default one, but if it doesn't suit your fancy, try the rebel. I personally like the commissioner.

It's probably your internet. Cyclone is a very swift killer and my personal choice (with exmags because the COF is incredible without it, and 10 more 167 damage rounds is a HUGE boost).

Infil and LA require a lot of familiarity with the territory you're working in. Just give it time, and never fight a fair fight. Cloak and bail if they spot you, after laying a mine where they think you are of course

Its OK, Its all so because u slowpoke