Gaining

Sounds to like you need to get that depression in check, so you should see a doctor !

Bonus is that many of the antidepressant-drugs are promoting weight gain.

So I think that should be the way to go.

Other than that eat everything with the Combination of fat and carbs/sugar !

My favorite way to gain weight is to have a big meal right before bed. Your body doesn't have time to use the calories or fat you just ate. So it stores it.