First, check your bed. Lift up the sheets and check the very corners of the mattress. I'd also make sure to get a blood test specifically for thyroid as well as Lyme disease.
In the interim, try washing with unscented detergents and unscented fabric softeners.
Best wishes, a rash can be very frustrating.
Thank you. We switched to "free" detergents for clothes a long time ago. I've checked the beds and we've bought a new one [we have a vacation home I checked, too.]
I check the beds at hotels now. All the time.