Positive OPK, period due tomorrow, pain

Okay so I am having a lot of pain in my right side and I feel pressure (almost like I have to poop, but I can’t). It almost feels like ovulation pain, but I am on CD31 right now. I get periods every month but my period is due tomorrow. I took an opk over the weekend and it was getting close to positive. I took one today and the rest line was darker then the control line, and my pregnancy test was negative. I’m not trying to get pregnant, I had in the past but I’m really concerned. I am on vitex, metformin, and a multivitamin. I do occasionally have unprotected sex with my long term boyfriend. I’m confused. Would it be possible I’m ovulating twice this month? Or is it possible to get a positive right before your period. HELP!