How do you treat psoriasis?

See a dermatologist. There is a med school right in your town. You will not need to look far. Steroid creams are basic. There are a variety of other things. You need an individual evaluation. It is not your diet, not your nerves, not an allergy, not contagious. It is a genetic trait.
First make appt to . see dermatologist, second it really depends on severity of psoriasis and the type. We typically start with topical steroids, vitamin D, retinoids, then UV treatments depending on skin types, oral medication, injectable therapy. But see derm to discuss options that are right for you.