Antibiotics

Common antibiotics that I know is penicillin or streptomycin. What are antibiotics for or where they derived from? Antibiotics are being used to prevent any kind of infection from spreading or getting severe. This substance derived from certain bacteria, fungi and other microorganisms that will fight for other microorganisms that is growing in our system and usually get us sick. I am taking some certain antibiotics right now to cure my sinus infection. My immune system is not immune enough to any bacteria that goes around at my job. Accordingly its takes a year for you to get immune with all of those bacteria when you work at preschool or at the health care. I am bothered of getting sick every 3 months and its keeping me running a lot of errands. I cant rely forever with antibiotics It might not work in my system one day.