DRY COUGH AFTER STREP THROAT....HELP?

I had strep a week ago, and after finishing the antibiotics and feeling 99% better I developed a cough and alot of post nasal drip. each morning i have to hack up some phlegm and its just nasty. the only thing that seems to calm the cough and bottom of throat irritation is food. Is this normal. ? or could there be a strain of strep still left thats turning into walking penumonia. i've been like this for 12 days.