I’ve worked in primary schools for 10 years. The first couple of years I got regular illnesses colds/ flu/ tonsillitis etc. For the past 7 years I’ve barely picked up a cold a year. However, since going back in September I’ve had continual colds 
. As soon as I feel better for a few days I start brewing another one.
The one I’ve got now is awful and I feel rotten. Not covid, just continual bad colds. I can’t take time off every time I have a cold of course.
My diet or environment hasn’t changed and I’m only in my thirties. I eat pretty healthily and take supplements including C and D.
What could be going on? Any tips of advice appreciated.