Okay So, I Hardly Masturbate, Maybe Once A Week Or

Okay so, I hardly masturbate, maybe once a week or once every two weeks. I don't put my fingers inside me, I just rub my clit until I orgasm. The past few times, I've noticed I would bleed a lot directly afterwards. I'm on my depo shot so I don't get my period, just spotting but not that much blood. What could it possibly be? I have to wipe multiple times to get all the blood to go away. And even then, there's still traces of it hours later.