I NEED HELP!!

every time I masturbate I bleed. My fwb says I should get tested but I’ve only had sex with one person and it’s him. I thought it was just because I was too small inside so the friction was causing me to bleed. It doesn’t happen when I finger myself, and I looked up possible causes of vaginal bleeding and I just don’t know what to do! Google said it could also be because of birth control, I have the Nexplanon or the arm implant. I’m scared please help!!!