What type of secretion? thin like drooling or thick rope type mucus, maybe yellowish? Radiation can sometimes cause "hypersalivation" and reduced clearance of saliva, so can an oral infection cause this. On the other hand, the thick rope muscus is caused by the destruction of thin saliva produced by the salivary glands, mainly paritoid. Until the glands start recovering, which was about two post treatment for me, you will have the rope mucus, which is common.

As suggested, keep rinsing, sleep on an incline, use a humidifier, drink liquids, mucinex and robotussm help some, rinsing with papaya or pineapple juice or seltzer breaks up the mucus, even meat tenderizer diluted in water to rinse with. Good luck.