Really big issue 😭

So my boyfriend and I started having sex right after I finished my period in July, we had unprotected sex and he came inside of me! I did not take a plan B, and I'm NOT, nor have I ever been on birth control. August came around, it was about the 12th 13th that we had multiple rounds during the day, at night, in the morning. Every single time he came inside of me and we had unprotected sex.. by the end of August I've realized Ive missed my period completely and I take TWO pregnancy test. BOTH come out negative. It's September already and I still haven't gotten my period. I need to know if I'm pregnant or not before my boyfriend leaves to the army September 11th !! What should I do!!???