Hello,
I do feel for you, having nursed many hundreds of men and women through the experience of hair loss.
It is plausible that you hair loss could have been brought on by stress or even the excitement of starting medical college. There are some products on the market which help reduce hair loss, however they will not help unless you cut your hair very short.
The daily pulling on your hair can weaken the hair follicle, sleeping on long hair tangles it and by brushing it in the morning you pull more out. Washing your hair has the same effect. Basically due to the length of your hair you are literally pulling it out of its socket.
I do realise that your long hair is your glory, but consider having it cut really short. I don’t mean a few inches off; I mean really short, a short bob or a short layered cut. This will give your hair a break from being pulled daily and therefore a chance to recover, especially since your only 22 years old.
If you do take the plunge and go for a shorter hairstyle then I suggest you use specialised shampoos and conditioners so that your hair can recover from the daily pulling and can grow back thicker. Philip Kingsley has a great selection of hair care products which you can buy via the Internet. I recommend you try Philip Kingsley’s special dietary supplement PK4 hair, this may help you but whichever way you go, your hair needs to be cut short, a trim will not work!
I know my advice is not what you want to read, but to be honest it is the only and best advice I can give you. By cutting your hair short, then and only then will your hair recover.