Bleeding during sex

Since I had my child 3 years ago I have been having all kinds of problems. I haven't been able to get pregnant since then and I'm not using any kind of birth control. When I went to my doctor he said it was endometriosis. I used to bleed alot in between periods and when having sex. I don't really have any pain. Every now and then I do have pain in my lower abdomen. I don't have any pain during sex. Now I'm not having any irregular bleeding but still bleeding during sex. When I went to the doctor I did have a bacterial infection and I was treated for that. But I 'm still bleeding when I have sex not all the time but enough to make sex uncomfortable, not knowing when I will bleed or not. I don't know what is causing  this.