Question about bra sizes?

Ok so this is prob gonna be TMI. Sorry. Anyways, right now i am a 36C in bras but all my bras seem too small. I feel like my boob is about to fall out. I don't have a tape measures at my house so I can't be sure, but I measured the distance with my fingers and used a ruler (lol) and it looks like 4 inches, which would be a D. But my boobs are really pointy so I know I would not fill a D cup and there would be a lot of empty space. I told my mom but she didn't do anything. Should I just deal with a C until my boobs uh..round out? I'm 14 btw. My mom doubts that I am a D because she is a C but the C cups are already too small and I feel like they kinda squish my boobs in. Should I go get measured to see if I need a bigger size or if I am wearing the right one? The bras are not uncomfortable but I just want to wear the right size bra. Thanks for your help(: