Losing hair at 15!!

I am a 15 yo male. I have no other health problems besides this hair loss. My hair used to be quite thick as a child, but now it is quite thin. It started when I was about 13, getting progressively worse. I scheduled an appointment with a dermatologist, but it's in January and I would like to do something about it now. My hair is thin all over, but esecially on the crown and the complete top. If I gel my hair, my scalp shines through being easily seen. Even with dry hair, my scalp can often be seen. My hair is also getting thin and whispy around the thinning areas. There's two things that could be happenning. I could be losing hair, or my hair could be getting thin and weak. Are there any herbal supplements that can help me? Would it be harmful to use rogain before I'm 18? Could this be caused by excessive testosterone? Any advice or help would be greatly appreciated, it's really a problem at my age. Thanks