Hey there I have psoriasis on my scalp too. if people think its dandruff let them think it because they probably dontknow what psoriasis is.
Any ways I went to the dermatologist and he gave me some oil. I think it is called Derma-Smoothe. You put it on at night with a shower cap. and wash it out with shampoo in the morning. it works pretty good its just that you have to have a consistent use.
I use it one night (with a showercap)
I use it as a hair styling oil the next (I do not wash it out)
The day after that i wait till night and put some more on with a shower cap.
I hope you find something that works. If you read the other post you may find something helpful. GOOD LUCK!