Has anything in your routine changed? I know that once my son started karate, he was getting sicker due to the added exposure to contaminated surfaces (the primary suspect).
I have forcefully developed habits that essentially prevent transmission via public surfaces; ex. I push open doors with my fist, or pull them open with my ring finger, key interac pads with the same ring finger (the finger I'm less likely to stick in my mouth or eye).
This combined with a few supplements I take daily (1Tb coconut oil - for the lauric acid, 1000mg krill oil, 500mg enteric coated garlic pills) has me feeling pretty damn good. Vitamin D is also huge - I take 4000UI/day. The amount of microbiological processes that need D is staggering and there's no way the typical doctor recommended dosage is enough.
When I take a multivitamin, my urine glows. When I take the above, my urine is clear, because it's all getting used.
This lady is brilliant and is the source of my info. Her credentials make your average doctor look like a kid from the 'special' class.