I agree with @Isaiah_40_31 about the IJV compression, & the C1 process looks pretty big & very involved…Your symptoms do sound like IJV compression and possibly intracranial hypertension too.
There’s info in this section about symptoms & possible causes if you haven’t seen it:
Your IJV does look quite broad lower down your neck, I wonder if there’s some compression further down, have you looked into TOS symptoms?
It’s a shame we can’t see your hyoid on those scans, although hopefully @TML can take a look at the axial clip, I’m not very good at reading those.
But certainly as @Isaiah_40_31 says, it’s worth trying to see Dr Costantino, as he would be able to see what we can see on those scans, just so frustrating that the other doctors you’ve seen & the radiologists couldn’t!!