With respect to the weight gain. I recently had a food allergy test and found out I'm Intolerant to mammalian fat proteins ( basically if it has 4 hooves I can't eat it or drink it's milk )
I'm also intolerant to wheat.

So I'm left with Turkey and chicken. Some grains and a whole load of veggies .... which I hate.

But over the past few days I've discovered I'll eat almost any vegetables raw ! ... Im eating sugar snap peas;, carrots and swede/turnip all cut into sticks and dipped in houmous as I'm typing.
I defy my body to put weight on while I'm eating like this !! Seriously it's absolutely delicious.
And at night when those seroquel munchies kick in its definitely a great alternative to chips and candy !

I also recommend getting out for a walk. I know it's easier said than done but once you're out there ... pretty much guarantee you'll feel good and serotonin levels will increase naturally.

A contributing factor to my current dip in mood is I've just had one knee operated on and due to get the other one done in a few weeks.
I was walking 10k and / or going to the gym 5 days a week because I'm very over weight already. Thou I went from the size of a small house to maybe a 2 bed apartment ( lol !) So I was fat but fit.
Going from all that to not even being able to walk 500 yards to the local shop since last August has been very hard.
.... ... and my weight is a massive trigger for me.
In spite of many changes in diet nothing has helped me shift any more weight. But tbh I figure given the meds and zero exercise I'm doing great having not gained any weight.
Fingers crossed cutting out the meats/dairy and wheat might finally make a difference.

It's not easy and our mental health and the meds etc
... yep it all sometimes feels like just swapping one set of challenges for another !