I'm also experiencing hair loss due to having gastric bypass surgery - almost all of those who have the surgery have some hair loss for months afterwards. I wasn't concerned about this side effect at first since I had so much hair to begin with. But now I'm really annoyed by losing so much hair (even though no one else notices ...it still looks like I have plenty of hair). So I just started taking Biotin, which is the most common thing people suggest taking in the world of bariatric surgery. I don't know if it will help or not since I just started taking it myself. They say it has more to do with protein intake than anything else. I'm not saying that's YOUR issue, but that's mainly the issue with many after the surgery.
I would talk to your doc as others suggested. You just never know whether to chalk it up to something like stress, or whether it's of more concern to your health.