Help! I need advice.

My periods are always very heavy, and I experience serious cramping. My cycle is normally 35 days. I am a week and 2 days late, with all of my "normal" period symptoms. I don't feel pregnant, and I've taken 2 tests, both negative. I only had sex 3 times last month, all times with protection and withdrawl. I decided to start taking my birth control pill last night, but still nothing. I am not sure where to go from here!