Bleeding a couple days after sex

I just had sex for the first time on the 30th of December, and I started light bleeding then I had sex again on the 2 on January. And the first day it was light red like mucusy (if that's a word) sorry for the grossness, but I'm a little worried. But now it's turned a bit brown, and I really don't know what to do. I had protected sex and he pulled out so I don't think I'm pregnant but I don't know what could be causing this?