The state you live in makes a difference since the laws may vary. Also your age. For example, in New York, it is illegal for any doctor to give a minor patient information regading any sexually related treatment to the parent if the child is 12 yrs old or older. There are some medical decisions your mother would be able to make since you are a minor, especially in the cases of emergencies because at your young age, you dont necessariliy understand the ramifications of such decisions. But in the case of sexual or drug related treatments, you may have a leg to stand on here. You will need to do a searh for 'patient confidentiality for minors in *your state*'.
The next question is, if you find out your rights are being breached here (personally, I think they are but then again I dont know how old you are) what can you do about it? You dont want to start making a scene and saying you are going to call the police or child protective services because that simply doesnt sound like a mature girl making her own decisions (although CPS may actually be an option). You can possibly go to the doctor and say something like "I wonder what the AMA (American Medical Association) would say regarding my patient confidentiality rights here." It is a sound, calm yet mature "threat". But do your homework for your age and state.