I usually do nasal irrigation before bed when I have congestion, that helps a lot.
And when it gets really bad I use a nasal spray to get a propwr night's sleep, but you need becareful with those as your bidy can quickly become addicted. 
Normal otc decongestant also works well. I prioritize sleep quality over 'not using medicines' as that's how the body heals itself.


But, after switching to a almost no carb diet and working out a bit more, I haven't gotten sick in years. 
Occasional sore throats but they go away quickly.