HELP!!

I have had my period for about 4 years now and about a year ago I started to have really bad cramps to the point where I would cry and get so sick I couldn’t keep my food down. I have gone to the doctor about it and they said they will see how it goes and if it gets better(which it very slightly has). The problem is my mom won’t put me on birth control at all because she thinks i’m just using it to have sex with my boyfriend, which she has seen me get sick because of my period many of times and thinks i’m faking it, but she also knows I am sexually active. I have tried to get her to get me another doctors appointment but she refuses to. I have gotten prescribed medicine for my period to make it better and i’ve tried everything but nothing seems to work. can someone please help give recommendations on how to make my period more tolerable or how to help convince my mom to put me on birth control!!