Below is a link to a fairly recent post with some good info and recommendations.
I lost alot of hair after my 2nd major surgery, which was only 13 months after my 1st major surgery. I don't recall losing any hair after my 1st surgery, but going into the 2nd surgery I was very, very sick with anemia and lots of inflammation due to Crohn's Colitis. Pile on more anesthesia and that 2nd time I ended up on Coumadin for bloodclots. Not sure if it was one thing or a combo of things for me.
My worst loss was the top of my head, bangs and sides around my face. I was beside myself and wore wide headbands to cover. I started taking Biotin and immediately I started sprouting hair again. Now, a year and a half later, it has all come back