Wheatgrass juice and probiotics. A wheatgrass shot used to be my go to when I was prone to respiratory issues (there were several years in my 20s where I had three or four bouts of bronchitis a year. It was awful). I would take it when I felt the beginnings of it (once I learned the trick), and by the next morning, I was fine. No bronchitis! You need a special juicer for wheatgrass though, so I don't know if it's a common thing where you are. Some warnings if you ever try it: it's not super pleasant. It's like drinking a shotglass of liquid lawn. But worth it to not be sick, so I plugged my nose and downed it. It also made me belch all night after, lol, which somehow tasted like carbonated lawn. Two, a juice bar will give you a chaser (or they do here, anyway), but DO NOT drink citrus for several hours or maybe a day afterward or it will nullify the beneficial effects. Jamba Juice (a juice bar) here gives you an orange wedge chaser, so I would always ask them for something else.
But I'm allergic now (naturally!), so no more wheatgrass for me. Which is ok, because I never get infections anymore (thank goodness).
Probiotics, the more strains, the better (so, a pill claiming one billion per dose but only three strains is not as good as one with ten strains but lower numbers of them per dose). But of course, you don't need pills to get probiotics in your diet. The way they work, is basically, they fill your gut (which is a huge player in your immune system) with beneficial bacteria, which crowds out bad for you bacteria as well as yeast (so people prone to yeast infections benefit from it, too).
I hope you feel better soon!!!
Oh, and PS - you CAN get wheatgrass pills, but fresh (drink within fifteen minutes of juicing) is more potent. But if you can't get fresh, the pills and powders are available.