So my girlfriend and I were having sex while she was on her period, and on the birth control pill. She said I could ejaculate inside her and in the heat of the moment we were both okay with it. Once we finished we were both freaked out so we went to the pharmacy and had her take a Plan B one-step pill within 30 minutes of having sex. Needless to say we are both alittle worried there's a possibility of her getting pregnant.

But with all those factors added in, is it even possible for her to get pregnant? And what are all the possible side effects of taking Plan B, while she's on her period, and taking the birth control pill religiously? Can one cancel out the other?
I'm sure it's painfully obvious I'm pretty nervous about this whole thing but I need some straight forward answers.