What Causes A Delayed Period,abdominal Cramps And Sore Breasts?

I think I may be pregnant, however I received a negative HPT and i went to the Dr and their test was negative too. I was on antibiotics in December and January which reduced the effectiveness of my BC and I spotted once in January and havent bled since. I am tired, my boobs are sensitive, abdominal cramps, sensitive waistline, and more frequent urination (about every 20-30 minutes) my blood count is fine with no infections. am i pregnant?