Welcome, Kate! Glad you found us. I was diagnosed with MG back in the 1970's. I never had a thymectomy, the neuro felt my MG was so mild, and of course, we had no insurance. MG is indeed a very individual disease, very definitely NOT one size fits all.
I only take Mestinon. You'll have to arrive at your optimum dosage on a trial and error basis. When I first started on Mestinon, my neuro told me to begin with 1/4 tablet, 4 times a day, and add 1/4 tablet each day until I got overdose symptoms, and then drop back down 1/4 tablet. I finally ended up with 1/2 to 3/4, depending on how tired I was that day, but I overdosed so easily, and my MG was so mild, that I basically went without Mestinon for years, just controlling my fatigue by resting and pacing myself.
In recent years I've had to start the Mestinon again, and now take 1 tablet every 3 or 4 hours, plus 1/2 Timespan at night.
By the way, Timespan is not supposed to be broken, though the occasional neuro will recommend 1/2, and I break mine in half with my doctor's blessing. (GP, though, not neuro). So I'm NOT suggesting you try breaking a Timespan, just mentioning I do it.
How much Mestinon do you take? Have they started you on any other medications? It is possible you will go into remission after the thymectomy, but the experiences of others have been that improvement comes slowly, over a period of months. You will probably not experience any drastic, sudden improvement, and may not improve at all, unfortunately.
Keep us updated on your thymectomy! Hope it goes well for you, and you have a speedy recovery.
Hugs,