Overtraining is a culprit. I can do cold, wet, etc. and am normally fine, except when overtired.

Allergies also crept on me in the early 40s. Don't know where you are, but... they hit you and you don't expect them. At the same time, I got all these respiratory infections and was sent to ENT, Pulmonary Function docs, asthma guys, etc. Turned out it was reflux and with a change in diet, tilt of the bed and proper medication, that symptom cleared up. Turns out lots of the throat and lung and cough was reflux, which even got sinus involved. Make sure they look at that.