My 7 month old is always sick, what do I do??

My 7 month old son has been sick 3 times in the last 30 days. First he had croup so I took him to the doctors and they gave him steroids, then 4 days after he got better he got bronchitis, so I took him back and they gave him Abrutol, antibiotics, and another steroid, after another week he got better and now 1 1/2 weeks later he has a stuff nose and a cough and has really thick pl-hem. I have heard that when you take steroids it kills your immune system so you can get sick really easy from the next illness, does anyone know if that is true? I am kind of thinking of just riding it out and letting his body fight it on it's own to make him stronger because he seems off-ly young to be giving all this medicine too. Any one have any advice on how to deal with this???