I'm 14 And Have Had My Period For 3 Years.

I'm 14 and have had my period for 3 years. I weigh 135 lbs and I have lost 15 lbs since September. I get my period once every 3-6 months, and the most I've gotten it in a year was 4 times, in my first year. When I'm on my period, it's brutal and I cry a lot. Normally I get really bad back pains. I want to go to the gynecologist but I live with my dad and since I don't have a mom or sisters, I don't know how to deal with this or cramps or periods or how to ask him to go to one. Please tell me what's wrong with me