immune system

I seem to cough a lot in public settings like gyms had a talk with my doctor about it and she thinks it has a lot to do with bacteria that my body is reacting to is there a supplement I can take before the gym that can help with this cough or change how my immune system acts?

what are the vitamins that were are missing that I should be getting? Something like vitamin C I read is good for immune system. So if I were to take it daily would that help my immune health? What about other vitamins? Seems like if I were to buy each one it would cost a fortune. Is there a...