Possible Pregnancy. Crazy. help please!

Hi! I was wondering if you can help me determine if I may be pregnant or not. My period is late - very late. I am not exactly regular, but for the past two months (January and February) my period had been pretty regular. It fell around the 17th both months. I still have not gotten my period since February 17, and it is now April 3. I have had unprotected sex, as my boyfriend and I use the withdrawal method (I know, not the safest). I believe it may have happened the weekend of the 18th. I have also been having weird cramps the past few days, and don't know if it is my period coming or not. But still nothing. I also tested negative on a home pregnancy test about a week ago, and don't know if I should retest or if I'm going crazy. Help please!