What Causes Bleeding Post Intercourse?

Hello. I've noticed recently that i bleed after intercourse. But i think now i have a cervix infection because of that. The bleeding was quite a lot, but it always stops immediately. I now have abdominal pain, which is like a burning aching feeling, my appetite has decreased severely, and i feel nautious. I think i'm starting to get a fever and i feel very weak and achy. I am 17 years old. my height is 5 ft 2 and i weigh 8.2 stone.