Does anybody know wats wrong with me?

Ok so I've been having some weird symptoms. A week after I got off my period I started 2 realize that I was bleeding everyday slightly. The first day I saw it, it was a lot! and days later it got a lighter but still kept coming. I knew it wasnt my period cuz I had got off a week b4. This went on for about another week. Then just a couple days ago it stopped but today wen I was having sex with my bf I felt the worst pain ever. I've been with him for 3 years and he's the only partner I've ever had(Im 18 by the way)I've never been in pain wen I had sex with him(except the first time)Idk wat it could be and I'm starting 2 get scared. The first day I started bleeding was after I had gone 2 a water park and went down a couple slides, idk if that has anything 2 do with it but wen I went down the slide I felt blood coming out of me so thats wat I thought it was from but wat does the pain have 2 do with it? Someone plz help! Im scared! And I kno anyone can say go 2 the doctor but I want 2 kno the reason why this is happening first or what caused it.anyone with personal experience?