I agree with splitimage about checking your iron, and perhaps Vitamin B as well. If you do (and you really should) go to an endocrinologist to talk about hormones, see if they can check your thyroid as well. They might be hesitant to because you're so young, but I am 22 and have had an autoimmune thyroid condition since I was a kid, and what you're describing sounds like what happened to me when I first got alopecia a few years ago (related to thyroid issues), which was a single dime-sized bald area that gradually spread outwards. I can totally relate to the fear, it's pretty nerve-wracking to watch. The good news though is you're recognizing it early, and so there is a lot more you can do at this stage with medical and cosmetic treatments, especially if it's only a nutrient deficiency that you could take supplements for. Talking to a hairdresser might help too because they know about hair-regrowing shampoos and other products (and can sometimes get you a discount!) But seriously, just focus on right now and don't let yourself react until you have an actual diagnosis, if there is one, because it's probably not a sign of a horrible disease or something. Even if it is alopecia, most people do not lose all their hair, and something like 80 or 90% regrow it within 6-12 months.