Cough Remedy for my 5 Year Old...desperately needed!?

My son has caught another cough and this time, it's getting to the point where I personally am about to give him cough medication, but the bottle says not for children under 6. Keeping the apartment cool does not help, the vaporizer makes the place damp, and he seems to be getting this cough because kids at school are getting sick left and right. It's not in is lungs, so we can rule out Bronchitis, but I so desperately need advice. I had to keep him home on Thursday because of a fever after a cough attack. I really need some sounds advice. My doctor is no help.