Borderlands is pissin me off! help?

I'm a lvl 26 survivor. On the kill taylor kobb mission.. the bandit killersand raiders, use to be Extremely. Weak Because I have strong weapons..but all of a sudden, one shot from A weakling bandit destroys my shield, and almost all my Health.. my sniper kills scagzilla in about 6 shots..but takes about 7 or 8 critical headshots just To kill one grunt.. they are too hard..what can I do? Not to mention trying to go in cover..they toss grnades. In..one grenade auto kills me