Period stopped then came back after sex

Olivia
I thought my period was over on like Monday because I had stopped bleeding and I wasn't having cramps anymore. Well yesterday my boyfriend and I had sex and a couple hours later when I went to the bathroom I saw that I had started to bleed again, and it wasn't spotting it was like heavy. Is this normal? Should I talk to a doctor? Kinda freaked me out a bit. Help!?