My son is on antibiotics, but new symptoms are appearing?

My 4 yo son (twin, 5 weeks early, pneumonia 4 times) was seen at a walk in clinic on Saturday for a high fever (104.5) he had for 2.5 days. He was diagnosed with an ear infection and given antibiotics. His fever broke Sunday. However, on Monday he started having a terrible cough, continuing today with the cough. He was tested Saturday for the flu (nose swab with answer back right away) and was negative. However, with the H1N1 virus, one thing warranting an ER visit (says the news) is being sick, getting better, then symptoms reappearing after a few days including fever and worse cough. While his cough is absolutely worse, his fever has not returned. Not wanting to be a neurotic mom, I need to know if his cough itself would warrant a revisit/ER visit. Thanks!