bleeding after sex???

so my bf and I had sex the last day of my period (he finished in me) then the next day I had no bleeding but when we had sex again I started bleeding for another 2 days so my cycle is 4-5 days and the bleeding went til day 8. But then the bleeding stopped and when we had sex again 2 days later I started bleeding again. What's going on ??? Why is this happening please help I'm getting worried ☹