The symptoms you just mentioned are classic. For example people can't tell I am smiling because my lips are straight line. My niece actually got mad at me because I did not smile at one of her jokes. My sisters left side of her face sags as the day goes on. As for the heat that always affects me. For me it is more the hot sun than the shower. The way I discovered that was a 30 minute boat ride. Thought I was in store for a trip to the ER. My blood panels went to Mayo, it takes a little longer but I trust them more than local labs. My first test was neg but the second one 4 months later was positive for binding but by then I was already being treated. My neuro-opto said he didn't really care what the first blood work showed, he was positive I had MG.
Good Luck
Mike