I am 17 i came off the deppo injection couple of month ago now i bleed unexpectedly and cramps during sex and then i start bleeding again?

Get checked: First, hopefully you are using condoms and another type of birth control to prevent diseases and pregnancy. Second, make sure you take pre-natal vitamins with Folic Acid to help prevent birth defects if you accidentally get pregnant. To answer your question, Depo-Provera can confuse your periods for a few months. If it's getting worse you may need to use medication to help with symptoms.