Well ive been to most places on the map i think and ive talked to everyone/done every quest ive gotten and ive still got to kill the super mutants, only thing is they destroy me, the ones with miniguns can 1 hit me, ive got 71 hp and power armour at the moment.

do i suck? have i missed alot of quests? do i have to grind?

While I'm curious about your build, nevertheless it's always possible that a super mutant will be able to one-shot you. The game's just set up such that critical hits can be, well, quite thoroughly critical. While grinding can help a bit with that, there's really little enough to be done about it.
If you grind, I say grind for cash to buy up as many scouting manuals as you can from the bookstore in the Hub. Learn that Outdoorsmanship until it's maxed at 91% from books alone, then (this is actually quite hideous) strategically use Buffout and Mentats to lower your Intelligence and Endurance through withdrawal symptoms, dropping the Outdoorsmanship back below 91% for the duration, and read even more. Once you've reached the very height of book learning in Outdoorsmanship, put a few points in the next time you level up.
There's other ways about this, but I feel this method will serve you the best in general.

What's your build? If you've done all available quests you shouldn't have to grind at all. Do you have all the companions? (assuming any are still alive)

Miniguns are nasty. If you're standing close to them, or they get a good crit on you, it's game over. When fighting a group of mutants, ALWAYS get the minigun guys first. Then the rocket launcher guys. After that, you can clean up the rest.

Have you explored the entire map? Did you get your power armor modified in the Boneyard? That helps too. You could also try turning down the difficulty or saving in every round of combat, to reload if things go badly that round.

I think I was level 12 or 13 the first time I finished the game. You can grind, if you want to, either on monsters in the wilderness or just by pickpocketing everyone, but it shouldn't be necessary to finish the game.

I never underestimate the role of cannonfodder (except the female, Katja?); Tycho can actually be quite useful. I just have to remember to stand behind cover whenever Ian fires. If they take hits instead of you, it's always a plus. I like to mentally give write around their death so they become heroes :)

Ian does fairly well so long as you don't give him anything with a burst-fire option. He does pretty well with the .223 pistol. Katja is actually pretty decent if you rush to get her early. Unfortunately usually by the time you get around to recruiting her you're fighting super mutants and the like, which are deadly for all of the companions. Tycho is the only guy I could consistently keep alive throughout the game almost every time. Just give him a rifle or a shotgun and you're golden.

If you think grinding is needed, head to the Boneyard (providing you haven't destroyed the deathclaw eggs yet!) and kill the three deathclaws on their map. Leave map, rest for a few hours, come back, re-kill deathclaws. Rinse and repeat until desired level is reached.

I'd also like to second the person who mentioned Outdoorsman. Many guides dismiss it as a waste of points, but it's very handy for avoiding nasty mutant ambushes.

It's strange.By the time you get your hands on a T-51b Power Armor,I suppose that even the most diplomatic build can survive in the wastelands.Anyway,critical hits always come by from time to time,and you'll die eventually,but it all should be a minor annoyance and shouldn't prevent you from progressing in the game.