Six year old has head cold and vomiting?

My six year old suffers from sinus issues. It starts out as a case of the sniffles. Then a full head cold. He sinuses are congested, stuffy/runny nose and cough. The cough seems to come from the mucus draining down the back of his throat from his sinuses. The drainage goes to his tummy and it makes him vomit. Its to the point that he has to stay out from school. Does anyone have any suggestions on what to do? Any remedies? Thanks for any help!!