Hi Dan. My case is similar to how you describe yours, although I also had chemotherapy and surgery. However my ten-years-after-treatment symptoms would read almost word for word like what you wrote.

My otolaryngologist assessed the lump as fibrosis caused by the radiation. Nothing to worry about. Hopefully your scan will show something similar. The only bad news is that's just the way it is for me - there's nothing to be done about it.

As for the coughing, I have started using one of those triangle pillows when sleeping which puts me in a more tilted position, helping drainage and marked reduction in coughing at night. The other thing that has helped is guaifenesen DM (Musinex). This makes my mucous drip drain better, and the 'DM' ingredient reduces the cough urge somewhat. I use it as needed, but take it most nights. Standard dose (400mg every 4 hours). My doc is not concerned about ongoing use.

Best of luck finding a way to deal with this. I'd be interested in anything else you learn that helps.
-Peter