A year or so ago I started losing tons of hair, but I had other symptoms (weight gain, acne, etc.) and of course it turned out to be PCOS. Since you don't seem to have any of these, I can't speculate.
I'll just say I know, I really do, how hard it is when your hair falls out. (I still have dreams about it to this day.) You are in my thoughts.
Keep a journal of your stress levels, food, exercise, and symptoms and have faith that you will get the answers you need as you seek them. In the meantime, remember that you are beautiful, inside and out. You are!