Already using nizoral shampoo?
http://www.hairlosstalk.com/hair-loss-treatments/nizoral/
If you want to use finasteride consult with doctor first. I would try and contact the doctor (you will need to ask to get an appointment with a dermatologist) to get more info and discover if it perhaps would already be possible at your age to have a small doses for example of 0.5mg every 3 days.. I don't think so but you can ask. If you never try you never know. A dermatologist can tell you what is happening with your hair and why. At your age I would advise you to make an appointment as soon as possible, perhaps it is something different than we all think.