Weight Loss from Meds?

Hi, all - new the forum here. I just wanted to see if anyone has experienced drastic weight loss from meds. I lost about 35 lbs over 12 months, with hardly any change to my diet at all - I was very skinny to begin with too, and now I'm really, really skinny. I have a large appetite, but can't seem to keep weight on. People are constantly asking me if there is anything wrong medically. My meds are Prozac, Lamictal, Geodon, Xanax. I started taking Vyvanse recently as well for ADD, which I know can cause weight loss, but I lost the weight before starting that med. I know Geodon and Prozac can cause weight loss, but my understanding is that they do so by suppressing the appetite, which has not happened to me, so I'm wondering why all the weight has fallen off.

I realize it's a plus to be underweight instead of the opposite, but it is concerning still. I've undergone extensive testing, including blood work and various other tests. Dr's have found no issues, for which I am thankful. Thanks.