Psoriasis, strech marks & black spots.

I have psoriasis from last 7 years. I am taking treatment from my dermatologist. At start I was put on steroid creams. Due to this stretch marks are came on my side of stomachs and on my shoulders & hands. Those r looking very bad on my body. Also because of patches black marks are developed on my body. Right now patches are under control and my dermatologist not giving any steroid creams. I was put on methotrexate for last 9 months. Recently he stopped methotrexate and again I am developing patches on my skin. With this chat I want to know how to control the psoriasis, really it disturbing me and I am at age to get marry. I know there is no permanent cure for psoriasis but atleast how to control it in a better way and how to get rid of those black spots & stretch marks. Is change of food habits and daily exercise will reduce psoriasis development. Is psoriasis exists throught the life. Awaiting for better tips and suggestions to control this irritating problem.