Hi, I am six days late on my period, I am on birth control but i missed two pills in the beginning of the third week of pills and had unprotected sex. I have been having head aches and slight cramps like I would have on my period but no bleeding, also my stomach muscle have been sore like i had worked out but hadnt, and my lower back has been hurting. I took a pregnancy and it was negative. Today i started having cramps in the side of my right thigh, kind of like a charlie horse but not as intense and has lasted for about 2 hours. It gets better when i sit down and am not moving it. could i be pregnant or is something else going on?