So about 3 weeks ago, I had unprotected sex, took the plan b pill. I then had unprotected sex again about 2 days later, and took the plan b pill again. I haven't been having any problems until today. I thought I was starting my period because I was having cramps, but every time I check to see if I've started, all I get is a little blood. I've heard of implantation bleeding , but I thought that could only happen up to 6 days after having sex .