What Causes Allergic Rashes On Body?

Question : Hi, I'm enquiring about rashes. I've broken out with a rash all over my body. About 35 years ago I was diagnosed with Seborhea(sp?) dermatitis(?). I had one flare-up and that was all. A few years ago I was diagnosed with psoriasis and still have several areas (small) that bother me. Now I've got this rash on the vulva area. both thighs, neck, back, both arms and even a few places on my hands. I've been applying an over the counter (Dermarest) and Cortizone-10. It is very itchy but not painful. I'm fine until something brushes against it and then the itch starts and becomes unbearable. The worst part of this is that I can't get any sleep at night. I'm up reading until 4 or 5 in the s.m. and then possibly fall asleep for a couple to a few hours, wake and maybe if I'm lucky fall asleep again for an hour or so. I'm 79 years old (will be 80 in November) and I'm also wondering if that has anything to do with this. My health otherwise is good, low blood pressure, no heart problems, etc. I'm on Levothyroxine, 88MCG; Timolol for glaucoma; Zetia and Livalo for cholesterol; plus I take a Calcium pill once a day, 2 D3, 2000 iu; and 4 PRN (fish oil for dry Eye Omega. I've got an appointment with a dermatologist for next Monday, but what can I do to elleviate this terrible itch until then. Any suggestions?a