seborrheic dermatitis into psoriasis

Hi, i have been suffering with Seborrheic Dermatitis since i was a kid. I am 20 years old now and still have it but at this time it became hard to control. i tried everything, all the shampoos, and all the methods on the internet, but nothing has worked. the problem with my skin is it's a combination between oily and dry (sounds stupid). Every time i try Seborrheic Dermatitis treatments such as dead Sea Salt or any prescribed or non prescribed shampoo, it turns into psoriasis, and it became harder to control. I have tried everything, including diet, sometimes water fast, but i haven't seen any thing that worked 100%. I am starting school in few weeks, and i don't want to be embarrassed about it.