I've been having this pain on my lower stomach and back, on the right side. I can't really run at all or it'll start hurting. It feels like a menstral pain, but it becomes REALLY sharp when I start to exercise. I've had a late period that came, FINALLY, last month(It took one and a half months after when I was supposed to start). I'm going to be starting my period November 7th. I also, had a yeast infection not too long ago (It was terrible). Yes, I'm sexually active, but I've been tested and I tested negative. Plus, I haven't had sex in about 7 months. It's TOTALLY out of the question, anyway!. But, these pains are terrible. I need some feedback, please. Thanks.

To me it sounds as though it may be infection related, possibly a kidney infection. You need to see your doctor for a definitive diagnosis and proper treatment.

You should check with your doctor it could be serious