im 13 and have sum questions about wen i masturbate

Ok, well, this is a kind of awkward subject for me to talk about because of my age, but I feel that I should try to get some answers. Whenever I masturbate, my abdomen will start to hurt, and I will start to notice a trace of blood when i begin to orgasm, is this normal? And after I am done masurbating, my lower abdomen will start to hurt, almost like when I am on my period, and I will have blood, but only for a little while, maybe slight traces for up to around an hour after, is it normal for me to have the blood? Or am I doing something wrong? I do push kind of hard sometimes, but do you think that is the cause of the blood? TFor the first 10-20 minutes, I feel really good, but then I start to hurt, am I putting to much pressure? Or could it be that I'm just not ready for that long of a "session"? Please help, I would graetly appreciate any responces, helpful or not, but please, do you have any ideas of what is going on?