I have major symptoms, but was told it is not MG.

I recently had an evaluation with a PT and after reviewing my extensive medical record asked if I had MG. I told her that I’ve been tested several times over the last almost 30 years but always told I do not have it.

In 1996 I had a large thymoma removed and was asked by the surgeon if I possibly had MG. Although I’ve been tested several times, it’s never come back positive.
I’m 70 years old now, and an experience daily difficulties with severe upper body fatigue, muscle, weakness, fatigue, when chewing food, choking very easily when I try to swallow, and the need for mobility assistance if I try to walk more than a few yards. I have been diagnosed with ocular melanoma (still in treatment), renal cell carcinoma, and thyroid cancer, (surgery 25 years ago). My left eyelid has drooped for many years and with the cancer my vision is very bad in that eye. My question is, “has anyone gone undiagnosed but still suffer major symptoms? If so, how do you cope?”