I'm not surprised that you're skinny, either, because I have similar issues and I am thin as a rail and always have been. When you can't digest food properly due to being so anxious that your stomach and guts are in a twist, then it's hard to put on weight and easy to get deficiencies in your diet.
Multivitamins may be a waste of money for most people, but for me they are just insurance against dietary deficiencies. That said, I only take 1/2 tablet a day each of men's multivitamin, B12 complex, and zinc, and also a vitamin D3 gelcap. Occasionally I'll take 1/2 of an iron supplement tablet too, since my iron tends to run a little low and there's none in the men's multivitamins, but I don't take this often because high iron can be a bigger problem.