Hi, I can't help you much about your inability to orgasm. The only way is to talk to your doctor. Anything you say to them is confidential. Does your mom always go to your appointments with you? I know it's hard but maybe you could tell her to step outside. Or if you have your doctor's number then you can call them and talk to them about your problem over the phone and tell them that you don't want your mom to find out or something.
Also, the part where you said "I mean we do have intercourse but I do it mainly for his enjoyment" really stood out to me. I don't have a lot of experience with sex but I do know one thing and that is that you should never have sex just to please your partner. It has to be both ways. You don't owe anything to him. You are not his property, you're not obligated to have sex with him. I'm sure you give consent and love him but having sex with him mainly for his enjoyment is not okay. You have the right to say no even you guys are together. I hope you know that.
Good luck with everything!

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