I can't think of any STD that would cause your symptoms. However, Exelderm is an antifungal, and I was going to suggest a fungal infection. Did it improve at all while you were using it?
It could also be eczema, dermatitis, an allergic reaction to just about anything that comes near that area - laundry detergent, soap, shaving cream if you shave, wax if you wax, toilet paper, some fabric in your underwear, lichen planus (though that usually causes bumps), lube, condoms, etc.
How far into January do you have to wait for the appt? The only things I can tell you to do, not knowing what's causing it and certainly not wanting to make it worse, are to use a gentle, scent- and dye-free cleanser, use scent- and dye-free laundry detergent, as well as the same in toilet paper. Gently pat the area dry after a shower.
If you are inspecting yourself, limit that to once a day at the most. You could be causing more irritation every time you look.
Call the derm and ask to be put on a cancellation list. This is a list that they might keep so when people cancel appts, they can call other patients and get them filled. Sometimes it means you have to be ready at the last minute, but it's worth it if it cuts your waiting time a lot.
Yeah, the holidays are probably pushing things back.
I'm assuming it's cold in Colorado right now, and given that it's reacting to hot and cold, and maybe sweating when you're sleeping and when you're exercising, I'd go with fungus or eczema. Do you sleep with underwear on or off? Try the opposite of whatever you do now.
If you get your body washes at the drug store or grocery store like most of us, try Dove Sensitive Skin Body Wash, or Ivory soap or body wash. Those are both very gentle. You can also try a soap-free cleanser, like Cetaphil Ultra Gentle Body Wash. Look at any body wash carefully to make sure it isn't loaded with scents you don't need. Our bodies don't need to smell like lavender or a rain forest.
My skin reacts to everything, and I use Tide or All scent- and dye-free detergent. Really, my clothes come out the same with both, and for me, it depends on which one the store has. If you use dryer sheets, Bounce has scent and dye free dryer sheets. Other brands do too, but I only do my laundry, and Bounce is the only one I've found that comes in the smaller size.
Since the cream caused more irritation at times, I wouldn't put anything else on it right now, and this will give it time to do it's thing before you see the derm on the 7th. If it's going to get bad, let it get bad so they can see how bad it gets for you. I know that sucks, but it may help you in the long run.
Good luck and let us know how it goes.