Don't worry, jd--what you describe certainly sounds like psoriasis and nothing more. Psoriasis, like most skin problems, comes and goes as it pleases. You can suppress it, but it comes back when it wants to. It is NOT and STD. The business about weak immunity is pure speculation, and in any case has nothing to do with HIV. When you see the redness, treat it; otherwise, ignore it.
Best.
Dr. Rockoff