I've had psoriasis for around 35 yrs. My dd who's 12 has had it since she was 6.
In my experience there is no 'one cream' that works. Specialists are still not entirely certain what causes it. For some diet can help but by no means all. There are also different types of psoriasis. I have Guttate and plaque. The guttate (penny sized red spots all over the skin) comes and goes, but the plaque type is always there and itchy and painful.
A pp said to avoid all steroid creams. For me, steroid creams are the only thing that has ever had any effect. However relief comes from extreme amounts of moisturising. My Dermatologist always says to me MOISTURISE! She says 80% of the people she sees to do not put enough cream on, enough times a day. Slather it on. I use a heavy waxy emollient along with things like Aveeno and it goes on at least 4 times a day sometimes more. I often use a sock to keep the cream to soak in (I have a very painful patch on my foot).
I've had scalp psoriasis in the past but am currently clear. I use TGel derm shampoo but when it was bad I would smother my head in emollient cream and massage into my scalp hours before washing. It's a pain but it brings a bit of relief. I've found that with patience the scalp will recover.
My dd was given UV light treatment when she was 6 by the hospital (she was very severely effected). It was 3 x week for 3 months. It worked wonders for her and she been relatively clear for 6 years. She also had/has scalp psoriasis but the side effect if uv treatment was that it seemed to clear her scalp too.
Sorry to bang on too long.
I would really recommend seeing a professional dr or even a dermatologist if you can. Many gps aren't specialised enough in skin, but it's a hugely complicated thing to treat and needs proper help.
If not, start by an extreme moisturising regime, and a derm shampoo like TGel. See how you go. Don't let anyone tell you they have 'the cure'. It may be for them but the chances your 'cure' will be different. After 30+ of having this condition I'm all too used to people telling me how to 'cure' myself.
Good luck.