spend the first few game days staying alive... and dont try and run and gun till you know the sounds of the game Listen... u can hear mossies.. trolls Gd's just some are a bit harder in Swamp. due to extra ambient noises. but clearly you are in plains so you have experienced this but not yet learned from it.. look (2 eyes, listen 2 ears) dont make so much noise..ie sneak a lot! if you are not sneaking they will detect you before you detect them..ignore the skill point stuff..
Tactics my friends Tactics.. maybe the one you are using works for one enemy but not another