It would make sense because of healing and scar tissue, even without radiation. The lymphatic system has been compromised and draining could be an issue. Allergy meds taken every day could also create different issues, depending on what they are. The "stuffiness" is usually too thick mucus that can't flow freely and gets laden with bacteria that grows in the oerfect environment of the sinuses. It is usually a sinus infection that the body can't quite resolve.

Likewise with the snoring. It can be muscle weakness from surgery or radiatiin. The jaw ends up dropping a little quicker and farther than it did before surgery and radiation. If you are waking up often with a headache, it may be time for a sleep study to determine if that's the case. They use biometrics to measure the lower jaw drop and can record if those snoring issues are caused by oxygen starvation/CO2 buildup. Both have the same effect.

Like most of what we go through, just aging can cause all of that and be coincidental to treatment.