Stormynight,
In addition to gaining weight, you need to make sure you are eating the right types of foods.
I'm sure you've noticed my avatar by now! <img src="/images/graemlins/ooo.gif" alt="" />
I had a gastric bypass to lose weight, and hair loss is a very common side affect because of the rapid weight loss, AND the fact that the weight loss is caused by not getting enough protein to begin with. (We are only left with a small stomach pouch - that is why in the beginning it is so impotant to drink protein shakes, because we just cannot EAT enough protein to digest). So you might think about whether your diet has enough protein in it. Also enough iron, vitamin K (potassium), and I think the other big one that can lead to hair loss is calcium (not so sure about that one though.)
Gaining weight back by eating lots of carbs is not going to do you much good as far as getting your hair back unfortunately.