Bleeding after masturbation?

I am 18, not a virgin anymore. My period ended a week ago and I masturbated using nothing but my fingers. I noticed some dark blood on my fingers after, and I thought it was just leftover period blood. The next day, I masturbated again and there was no sign of blood or anything, so I assumed everything was back to normal. But today, it happened again. The same kind of blood that looks like old blood was on my fingers. I wouldn't really say I was bleeding because blood wasn't gushing out. It just seems to blend with my cum when I masturbate. Nothing hurts. There's no blood when I pee. I don't bleed any time during the day, either. Although, my discharge seems to have the same old blood in it, kind of like I'm spotting for my next period (but that's not possible because I just got it, like I said). I'm not sure what's going on. Should I be worried? By the way, I haven't had sex in months. I'm positive the spotting has nothing to do with being pregnant.