Many of your symptoms do sound like MG, but there are also many other conditions that cause fatigue. That is why MG can be so difficult to diagnose. One of your symptoms in particular that sounds very like MG is the difficulty in holding your neck up. Weakness in the neck can be a biggie in MG. Has anyone tried the old "finger held above eye level" quick test on you? It's one that a lot of doctors seem to do as the first quick assessment of MG, given that the eyelids often show fatigue before other muscle groups. Hold a finger slightly in front of your face, but slightly above the top of your head, so that you need to glance up at it. Without raising your chin, look up at the finger. A myasthenic will have great difficulty in maintaining this upward gaze. Within just a few seconds, the eyelids will start to want to close.
If the blood test comes back positive for MG, you most likely have it. However, if it comes back negative, you might still have it. As I remember, about 20% of myasthenics are sero-negative. For your sake, if you have MG, I hope you are sero-positive, since the road to diagnosis for a seroneg MGer is a long and rocky one.
Hugs,