drastic hair loss

Hello Everyone,
I am a new member. I shifted to san jose about 3 months back. I am from kolkata. i always had thin hair but no hairloss problems. for the last two months i have had drastic hairloss so much so that my scalp is clearly visisble. I take vitamin supplements regularly.i have no internal problems that i know of. do u know ladies what is causing this hairfall and i want to know if this has happened to anyone else too?and what do i do to stop this? i am crying myself to sleep almost everyday.