I'm a virgin, but I don't have a hymen?

Alright, this is sort of embarring, but I don't seem to have a hymen. However, I have a lumpy tumor-like m instead. It's very difficult to explain, and I haven't seen anything like it online. It basically completely blocks the vaginal opening. It's tough, like a bone, and when I "suck in", I can see part of the vaginal opening. I can barely insert tampons. I have to use the super slim ones, but it still hurts. I have very irregular periods, as in, I can skip 3 months at a time, and have spotty to very heavy periods. I know this is not my hymen, because it's not a thin "sheet" of skin. It's just a lump covered in little nodules. Please, can somebody explain to me what the hell this is??