There can be a lot of reasons contributing to hair fall. Some of them could be stress, unhealthy diet , losing weight, genetic, changing your hair products and even blow drying frequently.
I had the same problem and even went to different dermatologists. It did not really do any good to me. I still have my hair falling .
I suggest that drink lots of water. Take some multi vitamin supplement especially formulated for hair skin and nail. Go for brisk walk thrice a week, it is good for blood circulation.
Good luck !