I played the flute for several years but sadly, it's been put away for many more years than I played it. I find it interesting that singing is painful for you as I experienced the same thing before my ES diagnosis/surgeries. My singing is mostly during worship at church so nothing professional. I'm a soprano & found that singing higher notes caused my throat & jaw to tighten up to the point that they were both painful enough I'd have to stop singing. I had hoped that after surgery that problem would go away, but it seems to have abaited only partially. I can sing one or two songs before I start to have trouble again. I'm only 6 months out from my second surgery (Dr. Samji did both surgeries) & was told it can take a year for all the nerves, etc., to heal post op, so I continue to hold out hope that the singing discomfort will subside completely with a bit more time. I did ask Dr. Samji about my singing symptoms, & he said he'd had a very few patients that had mentioned a similar problem. but he couldn't diffinitively say the problem was a result of ES.
I am so sorry your life has been so thoroughly impacted by something you have yet to identify. I will pray tht you will be able to get your CT scan ASAP & that it will help clarify what is ailing you. It does sound like you've been resourceful in how you've chosen to communicate both with your family & otherwise. It's my opinion that you won't do any permanent damage if you play in your upcoming gig as your pain is coming from nerve irritation stemming from the way you hold your jaw and use your throat when you play but probably nothing more than that.
God is good. He won't give you more than you can handle.