If it's myasthenia gravis, that would be good news indeed. mother in law has had MG probably since she was 19 years old. She's had symptoms tat long but was finally diagnosed about 30 years ago, just after husband & I were married.
Diagnosis - you'd be referred to a neurologist, or possibly an ophthalmic surgeon (for the possibility it's myasthenia ocular, which can be a preliminary stage to MG). The specialist would do a Tensilon test where you get a short-acting dose of neostigmine. This acts to help the nerve signal be more efficient in getting the message to the muscle. The test works well for about 15 minutes, ten you're back to where you were. But if it works and for that few minutes feel fantastic and things work well, then you will almost certainly be started on oral medications. It can take some time to tweak medications to the right dose.
If you take the Tensilon test and you don't have myasthenia, not only will it not do anything for the fatigue and the droopy muscles, but it can slow your heart rate down. But again - only for a few minutes, then it comes back to normal.
There are a number of treatments for MG. I remember that at one stage removal of the thymus gland was considered a valid treatment option. When mother in law had her hart bypass, they had to remove her thymus gland anyway. At her age the thymus should have atrophied down to nothing, but it was apparently the size of a grapefruit.
mother in law just turned 86.
I hope your doctor has a good specialist to refer you to. Or maybe your doctor can do the Tension test.
Let us know how you get on.
Marg