If you're on immunosuppresant drugs, you're going to be more susceptible. I don't think you can suppress and strengthen at the same time. As far as I know, the best you can do is what you're already doing... wash hands frequently, keep hands away from your face and avoid being around people who are obviously sick. You might look into that "Airborne" supplement, although I don't know how effective it would be while you're on immunosuppresants. You could ask your doc about
it.
http://www.airbornehealth.com/