Implantation bleeding??! (pic)

Hi:) I’m 17 and have recently started to have sex. I just started the pill on the 19th and my period lasted from the 16th- 21st. We had sex on the 27th and yesterday I noticed blood in my underwear:/ it was a mix of discharge, red blood, and brown blood. What does this mean? I do NOT want to be pregnant.

Ps- we’ve always used condoms and he has pulled out 100% of the time.