I want to be on birth control.

So I am 15 years old and an entire week before my period I get all the symptoms of having a period (cramps, mood swings, hunger, ect) but without the blood. And then I have my period with all those symptoms plus the blood for another week or longer. Its absolute hell. I have asked my mom about putting me on birth control for all of this but she just says that its normal and that she has been through worse. She also thinks that I just want it to avoid pregnancy. How do I convince her to take me to the doctor and put me on the pill?