I bleed everytime my bf finishes in me

Okay so me and my bf have been doing the nasty and lately he been finishing inside me and everytime after I start to bleed now last month I thought it was my period but it happened again two days ago and yesterday and I know I’m not on my peroidd bc I just had it so I wanna know what is causing it because I was on bc for the last 3 years and I’m worried that might be the cause eeven tho I been off for about 3/4 months