Odd bubble on my hymen

This is more then a little embarrassing but here goes. I am a proud virgin at 18. Just before my birthday I woke up at my cousin's house with the oddest sensation in my vaginal area. It felt as though somebody had stuck a marble in every time I went to sit up from bed. I checked and there was a giant bubble the size of the end of my little finger. I could see little blood veins in it. I was more then a little freaked. I called Telecare and described what happened and they told me to go see my doctor soon. I actually went horse back riding that day with no pain though. Later on I was sitting on my bed, reading a book trying not to think about my discomfort. When I got up I realized the feeling suddenly went away. My underwear was soaked with a small amount of blood and a lot of water. The bubble was gone but there was a small mark on my hymen where it had been. Since I have an exam with my doctor soon anyway I've decided not to go to some strange doctor on my vacation. But lately I've been having strange pains in that area. Like somebody's stabbing me with a tiny needle. I haven't missed any periods or anything. I don't know what would have caused that bubble. I called my mother when I found it. She works at the hospital but had never heard of this kind of thing before. I could not talk to anybody there about my problem. The only girl was my 15 year old cousin. I'm still a little freaked. The pains are pretty intense. I just want to know what may be causing it.