Blood after sex?

I'm on Depo and we've been having sex without a condom, for the last 5 months out of the 6 that I've been on it. He also finishes inside of me. Well we just finished again and when I wiped after peeing, this was on the toilet paper. This is the second time it's happened in the last two weeks but today it's more noticeable. Why would this happen? I have no forms of spotting on Depo (so spotting is abnormal for me) and we use lube (I can't self lubricate anymore because of the time that I was on the pill). We aren't really rough in bed either. Any advice?? Implantation bleeding? Too rough? Any help will be appreciated!!