Hi @scott519 The breathing passages are rather small. Any swelling in the back of the mouth or top of the throat can affect breathing. Also you have limited saliva which results in your airway sticking to itself and causing restrictions or the feeling of restrictions. Five months out you should be improving quicker than this. It wouldn't hurt to see an ENT for a quick check. This is just my lay-person's opinion. I had issues for months as well and saw an ENT, more to relieve my worries.
Sometimes it is just the feeling of restriction, the feeling something is stuck in the throat, the feeling something isn't right when all along everything is normal but the sensory feel isn't right. This is because the nerves there have suffered from the radiation. But in your case you are actually choking and must open your mouth to breath. This is why I recommend and ENT check.
We heal so slowly from radiation treatments. Are you getting better week to week or perhaps month to month?