Bleeding During Sex

What does it mean if you bleed during or after sex? I received this letter from Mariana: Please Help! Every time me and my girlfriend have sex we seem to bleed. And most of the time it's a lot. I want to know if we are doing anything wrong??? I can't figure it out. Any information would be of great help. Thank you very very much.

After eliminating the obvious causes, like making sure your fingernails are trimmed and you're not on your period, bleeding during sex can actually be a symptom of a greater problem.

What does it mean if you bleed during sex?