I had the exact opposite thing happen to me with
heat. The hotter I got, the worse the
rash, hives, itching, psoriasis got. Also sun, I accidentally got in the sun (and heat) for a short time one day and the psoriasis went wild.
The psoriasis is interferon induced (autoimmune disorder). While I hope yours will clear up soon with appropriate treatment, it is quite possible it will stay with you throughout the duration of treatment and even afterwards until the drugs are out of your system.