How to diagnose PCOS?

I am 29 years old - I stopped taking the birth control pill in February and started trying to get pregnant immediately. My periods started coming 35 days apart exactly, until last month when it was 5 days later. After coming off the pill I gained 15 lbs, got acne that I never had before and my periods are lasting only 2-4 days of light "dry brownish" discharge, with occasional blood clots? This month my period still hasn't come I am on day 45 since my last, but am still getting negative pregnancy tests. I wonder if I am even ovulating with these short periods, or could it possibly be PCOS? I was never told I had PCOS before, and I do have one child, but when I got pregnant with him it was on my first cycle after coming off the pill - so maybe my system was simply "jump-starting"? I am getting really frustrated - and I'd hate to think that I am wasting all these months of trying if I'm not even ovulating and need to be on medication or something. Also - I had a c section with my son, almost 2 years ago could this be causing my problem?