I have suffered from cholinergic urticaria for 2 years before I was diagnosed and treated just a month and half ago. The only thing that I could figure that changed was that I quit allergy shots before my heat rash started.
Luckily the allergy office that I went to was also a research office that specialized in the study of hives. The treatment plan he prescribed for me was Ranitidine, Xyzal, and Cetrizine twice a day. He also put me back on allergy shots, as having allergies is like giving a Coke to a kid with ADHD for cholinergic urticaria.
So far it has worked perfectly for me. After only a few days the rash quit, and I have not had one breakout since I started. For the past 2 years I lived in fear of just going near the dryer as I would be in debilitating pain. Now I have even joined CrossFit, and workout 5-6 days a week. I hope that this could help some people, as all of those meds are OTC and it worked for me.
(Disclaimer: Always talk to a doctor before trying medication or combinations of medications, as certain medications may not be safe for people who are pregnant, on other medications, or have certain medical conditions.)