i need help!!!!

okay so im 17 and i went on nexplanon in early october. the first month or so i wasnt bleeding but then i was bleeding everyday. me and my boyfriend would have unprotected sex at least once a week but he never came in me. wellin midnovember  i completely stopped bleeding except for once and that was today and there wasnt very much. the paranoid side of me has came out and im freaking out because i think i might be pregnant....what are your thoughts?  i took a test right before xmas and it was negative but im still scared. PLEASE HELP!!!