As I kid, I got lots of ear infections and tonsilitis; as an adult, sinus colds, post nasal drip, chronic coughs. It all stopped when I cut most dairy (I eat yogurt, ricotta and goat's/sheep's milk cheese) and most wheat.
On the yogurt . . . I forgot . . . the other thing to look for is "cream on the top" yogurt, which would indicate it has not been homogenized.