(Sharing because I'm wondering if anyone else has identified these as possible MCAS symptoms.)
So to deal with some of my obvious MCAS symptoms, my PCP and I increased my antihistamines according to the MCAS protocols. Then I decided to try switching from my morning Allegra to Claritin in case the Allegra wasn't working and that was worse so I switched back.
Beyond sinus, cardiovascular, and skin issues, there were two symptoms that I hadn't thought were MCAS that got better with extra Allegra -- IBS-C and severe sweating episodes. I'd had an IBS diagnosis (gas, constipation, and painful cramps) since 1990 and the sweating episodes had started after menopause. I thought the former was part of my fibromyalgia and that the latter might be related to POTS or hypoglycemia.
Also my hypoglycemia has gone away which is good, but I'm afraid it might just be converting to pre-diabetes.