Hi stealth
from what you have told me about your doctor I would say his competence is questionable, a diagnosis takes time, care and consideration of which he gave you 3 seconds worth, I would look for a new doctor in future if I were you.
If you are serious, about getting better its gonna take a little effort, here is some advice that worked for me:
i had the same probs as you when I was your age, hair loss and pitted nails, depression. At your age I would say it is a combination of stress, poor nutrition and a lack of enough good regular excercise.
I am basing my advice on that you are an average 21 year old with no major weight or other major health issues.
Everyone on this planet has stress, it's part of life, and there is nothing you can do to change that. The best thing you can do is build a body that can cope with stress.
Good regular cardiac excercise like jogging, cycling or even better swimming will build a body better able to cope with stress and once you are fit enough, stress will literally bounce off you. Think about taking up a martial art as this will keep you fit and you can make new friends.
If you're smoking take note, cigarettes are a false stress reliever, you can smoke a million cigarettes but it won't change a thing except make you unfit and sick. You can only fix stress by facing the issues that cause it and deal with them. My life is now awesome since I stopped that stupid smoking.
Also stress can mess with your digestive tract biology, I wouldn't be suprised if you have some digestive issues too. If you do, you should get yourself a product that contains digestive cultures (see your health food store as I don't think I am allowed to name a specific product brand?)
at your age I think your hair loss could be a nutrition problem, hair is made from protein, so you need to look at your protein intake. Eggs are an excellent source of protein and also contain other elements that aid and stimulate hair growth and hair strength. Providing you are not over weight or suffer from poor liver function you should be able to eat at least 4 to 8 eggs a week with no probs (quantity depending on your physical size), but you'll have to reduce fatty foods right down like cheese and butter so as not to overdose your colesterol intake. Apart from eggs you should be looking at the rest of your diet, cut out junk food, if you put garbage into your body, you will get a trashed body.
Also if you suffer from dandruff this will also reduce strength of scalp and hair folicles, keep dandruff under control and also check the shampoo you are using, most shampoos out there are full of nasty chemicals.
Anyway good food and good excercise and then if you are still losing hair I would start looking at genetics as the cause.
As for depression avoid drugs and alcohol, cause it will make it worse, once you are keeping fit and eating well you won't find time to be depressed, best thing to avoid depression is to keep yourself occupied, when you just want to relax and sit around rent a funny movie with some friends and have a few laughs and tell who or whatevers stressing you to get stuffed.
Hope you get better,
best regards
den