Bleeding after masturbation?

My son is 8 weeks old and My periods have returned. I was sexually frustrated for weeks it too scared to have sex because I had stitches. Anyway two days after I came off my period I masturbated and then I came back on my period. It was red for a few hours then brown for two days then stopped again. While I had my first period back it was very heavy nothing helped so I went on contraception and it stopped straight. Do you think it could have been leftover because it went from really heavy to nothing within an hour? It's been a week and I'm worried I'll come on again after doing it. Has anyone been in this situation or is it normal?