1) Cranberry juice, or cranberries, or their extract, taken daily. Chemicals in CBs keep many bacteria from colonizing, reducing infection. The effect(s) spread throughout the entire alimentary canal – from the sinuses, to the teeth/mouth, all the way through, etc. Just watch out for excess sugar, since the berries are sour by themselves.

2) Omega-3 fatty acids (EPA & DHA, from fish oil). Not vegan ALA from Flaxseeds. If you need to know why, do the research. Figure on 2-4 grams/day (net) of EPA+DHA.

3) Animal protein. Consider the possibility that your body needs more of the amino acids in animal proteins than you are getting. Some people get very sick on a partial or complete vegetarian diet. Assertions that vegetarianism is optimum for everyone are highly debatable (Paleolithic diet, etc).