Bleeding after I Masturbate, I recently got my depo shot

Hi I’m 17 and recently been receiving the depo shot of birth control I’ve had 3 injections so far and Recently after I  Masturbate  I bleed like 10 seconds straight after and I don’t understand why I’m still a virgin and I don’t put  anything inside me I just go around the clitoris and I don’t do it rough at all I’m to embarrassed to go to the doctors can someone tell me what’s happening please.... :(