I’m so sorry too that you’re back to feeling so bad…I agree that it sounds like the vagus nerve is causing some issues, if you read @GrnyAny’s post about vagus nerve healing you might see similar symptoms, and if you see how long it’s taken her to resolve issues then that might give you hope. It sounds also as if you could have Trigeminal Neuralgia or Facial nerve neuralgia causing the head pain, & maybe the accessory nerve is being irritated too causing the arm weakness.
If your symptoms resolved initially then it sounds as if the surgery was successful, we have seen other members whose symptoms have come back- whether it is scar tissue I don’t know, it’s worth reading up on that here as there have been posts about things members have tried, cold laser therapy being one of them. I think there have been other suggestions but I can’t remember off hand! I think some of the vascular ES doctors have removed scar tissue, I’m thinking Dr Hepworth has done that, more for IJV compression, here’s a link to one discussion mentioning adhesions:
Stylo-jugular venous compression- what to expect next? - General - Living with Eagle
And @TheDude saw Dr Hepworth also for scar tissue compressing the IJV:
Jugular vein compression after surgery - General / Eagle Syndrome Stories - Living with Eagle
Other members have mentioned muscle compression- the digastric muscle is a common one- if yours was cut during surgery is it possible as it’s healed it could be pressing on the nerves? The SCM muscle can affect the nerves too, & the omahyoid muscle, and we have had members who have had compressions by blood vessels and other nerves. As @Isaiah_40_31 says, a FIESTA MRI if you can get one may well show what is causing the compression if anything. I can’t think at the moment of any research papers talking about this, it’s more anecdotal from members on here. I don’t know that any other doctors would be able to see anything from your CT to know what’s happening, as it’s the nerves which need to be seen, so not sure that sending them to anyone else would be helpful…
Is there any chance you’ve overdone things whilst recovering, and now it’s set healing back?
I will try & find some posts on scar tissue, but sending you hugs and prayer that this will go as quickly as I came back 
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