Blood residue after sex?

Hey everyone so my boyfriend and I have been having sex for about 5 months, regularly a couple times a week. I'm on the pill, he cums inside me and everything works out fine. But twice now I have recently see a faint marking of blood on the toilet paper when I wipe after we have sex. It's very pink and I feel no pain or tears in my skin. Just wondering what this could be and why it's starting to happen now?