My last period was March 3-8 It is now May

Patient: My last period was March 3-8. It is now May 17. I have taken 2 hpt and both say neg. But ive been having lower back pain, breast tenderness, nausea on a few occasions, heartburn like crazy, and overly emotional for the past 3 or 4 weeks. I had my tubes tied almost 13 years ago so never thought about haveing unprotected sex with my husband and getting pregnant again. Could i be? And what are other possibilities that could cause this?