What Causes Cramps, Hard And Bloated Stomach And Missed Period?

Hi, I am currently not on any brith control. My last period ended January 2nd 2011, I had unprotected sex on the 15th of January, but I do not know if he ejactulated in me. I went to the doctors 3 days later and the pregnacy test was negative. I have not yet gotten my period although I am fairly irregular with the cycles. I have recently been getting heavy cramps and noticed my stomach is bloated and hard. Am I pregnant or expecting my period?