y is it that i get killed after 1 shot

everyone else is always cheating... isn't it obvious

Or, some people are just a lot better than you are.

Play more, practice. Have fun with the game.

To kill people easily with a minimum of shots, aim for the head, or upper chest/neck area.  A couple of shots in those regions will take people down easily.  That may be where you're getting hit.  Aiming is a skill, so start out by making sure you hit them, then walk your way around your target.

Before you know it, people will be asking how you killed the so easily.

My first inclination would be to think that they are probably cheating.  You should get a demo and post a link to it because there are several experts here that would be able to tell you for sure.

There is an extremely small chance however that whoever shot you nailed you in the head.  Shotgun, M60 and sniper rifle can all get a 1 hit kill in the head.  I believe headshot and neck damage is variable with headshots being up to 300% of the weapon's base damage and neck shots being up to 150%.

This whole cheating thing has gone on to far. Cheaters I dont understand whats to gain from cheating it doesnt prove or help anything. "Witch hunters" who relly cares just kick them off the servers Raven will do somthing about it. 1 more thing
it is posable to have "good days and bad days" heck sometimes I fell bad for having good days when there are lots of newbs on my server but it happends. Not everyone cheats like statted before get proof.
Sorry to rant and rave but SOF 2 rocks

DiD u get hit w/ a sniper rifle because most places in upper body make u die w/ 1 sniper bullet  
its a fact that sniper rifles are the most powerfull and accurate in the game so i they hit u in the upperbody or hit u in the head in 1 shot it would be most likley be a sniper rifle!!  it can be almost written down on paper!!!

or it could have been u had not much health left coz i've killed some 1 w/ an mp5 from long range and i wasn't cheating and they must have not had much health  

because i have been taken down 1 hit by a pistol but the only reason was i had a knife i had very very low health and the guy was running about every where