I'm confused

I'm 18 years old and my fiance and I had unprotected sex on May 26th and again on June 7th. My "period" came 2 weeks early and it was really heavy and only lasted 3 days when my period is usually really light and lasts about 6 days. About a week after the first night we had sex I've been experiencing mood swings, extremely tender breasts, a little bit of nausea and sensitivity to foods. Am I crazy to think I'm pregnant? I've taken two tests, one of them this morning. And both are negative.