If you have clinical mental problems getting drugs probably would help(there are multiple drugs so if one doesn't help another might). There are some promising drugless therapies being tried such as magnetics and deep mind stimulation you might want to research.
I don't know how bad your mental condition is but finding out if it's serious or not by talking to a professional might be a good step.
Otherwise. Exercise, cut fast food out, eat healthy and drink water. Make sure you get your electrolytes in with things like ultima replenisher.
Avoid canned food and anything with BPA or similar in things such as canned food, or clear tupperware. The less pollution the better you'll feel although you might feel terrible if you try a juice detox diet which might release too much toxins at once - better to go gradual on that.
Mentally if something is too stressful stop thinking about it. Take time to relax your mind regularly. If exercise is too much at first try stretching and
then work up to exercise. Cardio works good. Avoid stressful and negative people if possible. I hear people who believe in God are happier but
you'll have to look into that yourself.
I am not a doctor these are just things I researched myself.