I Have A Burning Pain In My Lower Right Pelvic

I have a burning pain in my lower right pelvic area about right where my leg meets and ive been taking flagyl. I was spotting for about three days and it started brownish red and then turned more brown before stopping. The pain is still there and im worried. I also have been having unprotected sex consistently for the last couple of weeks but ive taken 3 tests that have come back negative. What is most likely wrong with me?