My periods have seemed to have stopped and i have stared to get some bad pelvic pain. sex has even become painful. what could this be?

Concerning symptoms: In a young/healthy female who usually has no trouble with pain from relation and now suddenly has problem, it is concerning for a possibility of pelvic infection such endometritis, pelvic inflammatoru disease, severe vaginitis, uti/urethritis, or ectopic pregnancy etc...I would do a home pregnancy test and consult with doc for an evaluation as this is not normal. Good luck.

Could be a cyst.: The answer that would explain all 3 symptoms (periods stopping, pelvic pain and pain during intercourse) is an ovarian cyst, that is disrupting your normal cycles, and causing pain. You would need a sonogram and visit with gyn dr to find out for sure.