i've recently gone through the same problem.
when i would leave home my hair would stop falling out, when i got back it would start falling out again.
a few things i noticed: one, the water here dries out my hair and so it breaks off. i changed my shampoo and conditioner and it has helped a bit. want to get one of those showerheads with a filter but DPITA say's they don't work. also when i leave here i have access to fresh fruits and veggies and i think that may help too. diet pays a big roll in your hair, skin and nails.
since i cut 5 inches off my hair it doesn't seem like i'm shedding as much.
so what i'm saying is if you go to the dr and he/she says everything looks "normal" you may want to look at those things.
also, your hair goes in cycles. parts of the year you "shed" more than other parts of the year.