I have been having really bad cramps in my lower belly for over 2 months now. I also have constant headaches, I urinate abnormal times a day, and I feel tired all the time. I recently started been sexually active and I want to know if this could be a sign of pregnancy. I took a pregnancy test 2 weeks ago and it came out negative but my period had only lasted 2 days for the past two months. what can this be?