Uh..i dont know how to say this but..?

I'm 12 and on my period. well today i was felling some pain down there. i changed it and i don't know why but it started to hurt really bad so i looked to make sure it is not anything to go to the Doctor for and i found a big lump (inside you know what not on the outside) i cant touch it. it hurts like hell. and I'm to shy to tell my mom but if i have to i will... what do you think? its around the size of a quarter