What Causes An Intense Back Pain & Cramps?

i have a thyroid problem, as well as insulin resistance polycystic ovaries. i take metformin to help stimulate my period, ive been taking it for almost a year. it has helped a lot, i went from having my period a couple times a year if i was lucky to every month. i was also on birth control but stopped taking it around may of 2010. since being on the metformin ive had my period around the same time give or take a couple of days. in dec of 2010 i missed my period for a month, and didnt get it till jan of 2011. i should have gotten my periods a couple days ago. for the past 3 days ive been having intense lower back pains, yesterday i had intense cramps that didnt last more than a couple of minutes. this morning i went to the bathroom and wiped and saw a white discharge i wouldnt say it was a lot but it wasnt a little. i dont have protected sex with my boyfriend, i smoke both tobacco and marijuana. i dont drink and i am on meds for my thyroid, as well for my psychiatric illness, plus im over weight. whats going on?