Just something to keep in mind: one of the antibiotics used to treat Lyme is doxycyline, which is listed as a drug that can cause or worsen symptoms of MG: http://www.mginc.mb.ca/docs/MG_DrugList_Final-1.pdf
That said, I had Lyme a couple of years ago--not chronic, but a case that showed up a week or two after a tick bite (I had a bulls-eye rash, fever, and body aches). I took doxycycline because I didn't know any better, and neither did my internist. It didn't make my MG worse. As far as I know, it cured the Lyme--I was fortunate to catch it right away. I haven't had any fevers or body aches or joint pains since.