Hello and welcome to the head and neck group. Your husband appears to have some common problems with recovery and healing, which takes a very long time to overcome. There is help from this group for specific issues and ways to cope with irritation, cough, phlegm, etc.
My personal recommendation and experience is to get off of the opioids and on to OTC meds such as Tylenol. Although none of it is good for your liver and kidneys, Oxy will mess with everything that works in his body including the ability to think well. Digestive issues in particular, which can make overall health feel worse than it is, is the main reason I believe people take more of it.
Gage progress on a week by week basis. Perhaps record progress and issues in a calendar for trends. Seek out a physician for that which is not trending well. Ask anyone here on this forum for advice as someone here has certainly gone through pretty much anything you can imagine. Courage.