Not all people are meant to squat. However, in order to find out you must do some experimentation. The way you are currently squatting may not be the best for your build. You anthropomorphic build is different than someone who is 5'08 so you won't necessarily squat with the same form as them.
Read the building your raw squat series at this link:
http://www.lift-run-bang.com/p/most-...nd-series.html
He explains how to experiment to find the method (stance width and bar placement) that best suits you.
You might also try front squatting as your upper body will typically be in a more vertical position than a back squat. Front squats will kill your abs unless you are used to doing them.
Inversion will not strengthen your back. Deadlifts, back raises and hyperextensions will unless you have a structural anomaly that causes pain. Do you know the difference between muscular pain and structural pain?
If you can video yourself squatting and post it, we can critique it. I advise anyone who lifts seriously to videotape their compound lifts and review them. I do it between sets. Also, please realize form will break down as you near your max. Most people don't realize this and when they don't have PERFECT form on the lift, they freak out. If you don't push yourself, you won't surpass where you are now. If you can squat 275 now with semi good form and keep at it, when you get to 315, that 275 will look darn good. Go watch some powerlifting competition videos and tell me how good their max effort attempts look.
Also, if you wear a belt to squat, you do not tighten it as much as you can. You tighten it to the point where it is snug to tight but when you flex your abs, it makes it tighter. You may have to experiment with this a bit to figure it out. However, a lot of people like it tight as hell for the deadlift. For the squat, you flex your abs into to make it tight. That flexing helps maintain your arch.