brown discharge after sex

i’ve been on depo for over a year me and my SO had sex 2 days ago. this morning with i went to the bathroom i had some brown discharge. it wasn’t a lot or very dark but have had a little bit throughout the day also. when we had sex it wasn’t very rough or anything. we also had sex 8 days ago with out a condom but he did pull out. possible implantation or just old blood being released?