asking mom for birth control ?

okay so i'm 15 and I have a check up in a couple days just for school sports or whatever but I want to get on birth control and i just don't know how to bring it up to my mom. I am sexually actively and I have a boyfriend but we've always been safe , but I want it more because i've had horrible irregular periods since I was 8 and it was recommended to me when i was 9 but i was too young at the time ..
i'm just scared to bring it up to my mom because she's the type to think that it will only be because i'm scared i'll get pregnant🙄 
How do i tell her ? 

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