NeuroTalk Support Groups - still seronegative--is this even mg at all?

My second AChR antibodies test came back negative. Tomorrow I have a second SFEMG (first was borderline). The weird thing about my disease is that I have most of the typical mg symptoms mildly, but my main symptom--the one that really stands out now--is weak back and side muscles. I walk fine if I'm holding onto something (walker, grocery cart, shoulders of pre-teenage son, etc.), but otherwise those muscles are too weak to hold me up well. I tilt wildly back and forth from the waist up. But only later in the day, and not when I'm rested.

My arms and legs are noticeably, but not really bothersomely, weak. I had double vision a few times. Had a few nights when I had trouble swallowing. I can chew gum all day (!!) with no trouble. For brief periods during the day my neck is weak and my head gets tippy. But mostly it's the back and/or side muscles.

So, my new neuro doesn't think I have mg. So he's testing me for mg, because even though he doesn't think I have it, it's the most likely thing of all the things he can think of. They did the test for the enzyme that shows the msucles are breaking down, and that was fine. I've had MRIs of my head and neck--no demyelation. MG is the only fatiguable neuromuscular disease out there, right?

Tomorrow with the SFMEG I'm having some sort of test for LEMS. I think there's a blood test, too. But I don't have the tendon reflex signs of LEMS, and I'm not a smoker.

Any ideas? I'm getting discouraged here. What if they tell me it's psychogenic? What if I have some disease that no one's discovered yet?

Oh, and in preparation for the SFMEG, I went off the Mestinon. This is my second day without it. I thought I'd be weak as anything, but I feel just the same.

Abby