Down with Flu

I have finished my medication and a course of anti-biotics but my cough still remains unchanged. And it is not getting any better but added with a running nose. Looks like my system is resistent to the medication and each time when I cough, it takes weeks to cure. So I have finished my medication, now what. I have also been sneezing too often repeatedly. I have stopped taking Vitamin C as I have read that when you are down with a flu, never take Vitamin C which could aggravate the flu.