I see you're on Mirtazipine,*bytheway*, which does unfortunately give you an appetite. My daughter is on this AD, but as she is usually a skinny soul, it helps her keep her weight normal, and as you say, helps her to sleep. Could your GP possibly try you on an alternative?
Also, I have been doing Low Carb High Fat (LCHF) for the last 4 months, and my weight has dropped by almost a stone, with no effort (Yay!!)- the high fat helps you to feel full, and no temptation to snack. It's not a "diet" but a way of eating, and is wonderful for keeping blood glucose low.
It does mean rethinking food options, but once you get into it, it's easy.
It's not fat that makes you fat, it's the sugar (that includes carbohydrates in things like potatoes, bread, pasta and flour based food), might be worth a look at the low carb thread on here?