I had exactly the same problem. Psoriasis is exacerbated by stress, be that mental or physical, so any new training regime can cause it to flare up. However I found that after a month or two when my body got used to the new stresses I was putting it through and I got fitter the psoriasis began to clear up again. Hang in there and don't be put off by it!
I suffer too (but not badly) - may be worth visiting the doctor. I did a couple of years ago and he changed my cream (which I had used for years) and suggested an over the counter handcream to apply daily also