My boyfriend and I engaged in unprotected sex about 2 weeks ago and he did ejaculate in me. I had taken birth control for 2 days about 2 weeks before that but had to stop taking it because it gave me agonizing headaches. Well for the past 2 days I've had light bleeding, it's pink when I wipe and then brown when it's dried in my underwear, I've also been having light cramps and lower back pain. Could I possibly be pregnant and experiencing implantation bleeding?