Is the bleeding heavy and sudden w/o pain. If so, this could be something as simple as cervical erosion. It sounds bad, but really common. It is simply that the margin where the change takes place has shifted slightly and the lining becomes a bit raw as a result.
One easy way to think about it, is to think about your mouth. The surface of you lip is different from the surface of the gum inside your lip. At a certain point the two surfaces meet and change.
Imagine what would happen if this margin moved. You'd have some lining from the gum facing the outside world, exposed to the air. It's likely this would lead to a raw patch. This is the kind of thing that is happening in an erosion.
You can go to your gynecologist, and he/she can do a procedure to rectify the problem.
The sex is pretty rough and it has been a while since i've had sex so maybe that's it
Bleeding right after having sex it a very bad sign of a fungal or bacterial infection. The earlier you had it checked, the better for you. You and your partner should do the check up together though, because if there is any chance you have an infection, he also needs to undergo the treatment to avoid any chance of re-infection.
Are you lubed up enough down? Maybe trying some KY jelly during sex to moisten things up. Are you having super rough sex? Sometimes you could be tearing slightly and that could cause the bleeding. Is it painful to have sex? It may be a sing of an infection, so if sex is painful or you are bleeding alot you may want to see a doctor. I think the depo causes spotting, but I cant remember. Do you spot outside of your period and sex?