I don't get psoriasis but I have crohn's disease and you get some fun skin things with that sometimes. I don't get the really nasty stuff, but will get an eczema or something-like rash on my face around my mouth periodically. It also will show up on my shoulders from time to time. I have no idea what it is, and my doc assumes it's crohn's related. The only thing that clears it up is steroid cream. I also used to get (knock on wood) this weird rash in the sun on my arms and chest. Felt like little pin pricks all over the place. A dermatologist said it was PMLE, and said it *could* be related to the crohn's. But apparently those without it get PMLE as well. That hasn't happened in a couple of years thankfully. The only thing that fixed that was time (once I had a tan, it stopped).
There are new meds out there for psoriasis. I'm on one of them - Humira. I've been on it for 2 years (started out in a clinical trial). It's FDA approved for Rheumatoid Arthritis, in clinical trials for crohn's (but you can get it off label use). I believe it's still in trials for psoriasis also:
http://www.webmd.com/content/article/91/101441.htm
No, I don't work for Abbott

I actually hate taking meds, and went on a med vacation for about 6 months only to have it catch up with me. Humira put me in remission, among other things. Not sure if that's even an option for you, but I thought I'd let you know.
Good luck!