IHL, it is SO GOOD to hear that you are finally feeling a bit better! The first half of your post sounds so positive and clear-thinking. Of course, the rest of the post makes total sense after the nightmare you've been through with all the different treatments & reactions you've had!
Like everyone else, I don't know anything about
MCAS but would urge you to give your body a rest. Let it adjust to only the MCAS meds first and see how you feel. It can be scary worrying about
the "what ifs" of Lyme, but just try to let those thoughts slide for a little while as you get a bit stronger with this medicine that seems to be helping the most.
I posted on here in February that I'd been sleeping for all of 2015 and you guys suggested it was an allergic reaction to my latest meds. My doc agreed and took me off all meds to allow my immune system to get strong again. I had a raging response to total withdrawal: killer migraines and intense nausea that nothing could touch. (Except eating bananas, of all things!) After about
10 days of this I began feeling much MUCH better. I took 2 months off of meds and have started back on the mildest dose of abx. It's not giving me the usual herx/die-off/headache/exhaustion I always had before. So, even though I was scared of how my lyme symptoms might come roaring back, they did not. We are all different, as we know, but I wanted to share this in case it helps you feel more comfortable with the idea others are suggesting to take a little time off and then ease your way back in.
Best of luck to you, and of course, keep us posted.