Sounds a lot like myself. Just diagnosed with seronegative mg. Originally my eye doctor caught it and got the ball rolling to being diagnosed.

Had all the tests you have listed, blood work, EMG, SFEMG, nerve conduction, tensilon etc. and all were negative. Still show all the classic signs as you did. Neuro said I don't have it and Family Dr. said I do. Family Dr. started me on Mestinon last week.

I Took the first days worth under his supervision so he could monitor me. After 45 minutes my eyes began to water slightly and at 1 hr 15 minutes I noticed my right eyebrow shot upward like I was "eyeballing" someone. Then about 2 hrs in my left eyebrow was up about half of the right. My breathing (chest) improved, and the choking was not so bad.

I started on 30mg 3 times a day. Moved to 30mg 4 times a day now and will move up to 30mg 5 times a day next week. It takes me about 45 minutes to feel the effects and they fall off at 2 1/2 hrs like clockwork. So there is quite a gap between doses and from my last dose at night until morning. I am hoping to try timespan soon to help get through the nights. I would also recommend taking this medicine with food.

I will say that at the current dose I am fine until I become stressed or do any physical exertion. As this happens I can feel my eyes start to fall, my breathing get harder and just back to the way things are without it. Once I get rest things get better.

I hope this helps.