What Causes Puffiness Of Neck And Tightness In Chest With Myasthenia Gravis?

I have Graves Disease, Myasthenia, and possible Lupus. I am on immunosuppressants. The past couple of weeks, I have been experience puffiness on both sides of my neck, starting with the left side, tightness in my chest, and intermittent effusive sweating. Two days ago, I started developing a rash on the back of my right upper arm and on my side under my arm. The rash has now started the same way on my left side, on both knees, and my right upper leg. It starts out looking like little blisters, then forms into big red inflamed patches. It burns and itches. Any idea what this could be? Thanks