[Ydiss]

Seeing as you just started the game it's probably going to be this simple reason:

You aren't actually hitting them in the head when you think you are.

I don't know how skilled you are at these types of games but a general tip will be to keep your bursts short (when using automatic weapons) to reduce recoil. If you're using an SMG or MG and holding down fire until the clip runs out your shots will rarely hit target.

If you already are doing this, then it's gonna be simply due to the other players being faster at killing you (more accurate).

There are a number of cheats for this game, but (so far as I know) none that stop you taking as much damage as other players, or dealing more damage than other players.

My suggestion is, providing you enjoy the game, accept you're not quite as good as these players and practice until you are.

Another is to watch them in spectator mode and see how they play.