Can you be clearer about your diagnosis? You have both psoriasis and eczema? The first of course is an autoimmune arthritic disorder but the second is dry skin. The third problem is just heat rash, which is common particularly at the beginning of the hotter weather following winter, but is usually associated with outdoors activity because the gym is always similar in temperature. The problem with anyone helping you on here is that you have three different diagnoses for the same thing, and it's unlikely it's caused by all three, it's probably one of them. Because it comes and goes it's probably not psoriasis, which is chronic and can only be controlled by tamping down stress on your immune system, as this is the body attacking itself. Eczema can usually be at least moderated with natural lotions that keep you well moisturized. I get rashes from walking long periods of time outdoors in the winter because the skin gets dry in the winter and rubs against the long pants I have to wear that time of year. If I religiously apply my natural moisturizer it keeps it from getting too bad. In the hot weather, when I used to run, because it's very humid where I live as well, I used to get a rash from my legs rubbing together. Again, religious application of moisturizer and wearing bicycle shorts under my running shorts kept this tamed, though I hated running in those tight bike shorts. This can also be exacerbated by a diet too low in essential fats or excessively low fat diets, so you can try taking some flax seed oil or fish oil and see if it helps. But as I say, you cite three conditions that don't have the same causes or treatments, so that makes it hard for you to make a move -- your docs need to narrow this particular situation down so you can deal with it. My own thinking is that it's most likely a rash caused by rubbing of dry skin against other dry skin, but that's just a guess.
since it is work out related, heat rash?