Lately while I've been having sex with my partner I randomly start bleeding and a constant pain, like burning. I thought I wasn't lubricated enough so we started using it, but I still bleed and still have the pain. I went to the OBGYN and got tested for yeast and STDs and all came back negative. I don't know what could be causing this please help.

What did the doctor say to do about the bleeding?

They are not sure what is causing it.

They are not sure what is causing it.
If your doctor doesn't have an answer for you, then you need to see another one.