Do I have a sinus infection?

I had an especially bad bout of a cold/flu that lasted about a week. My doctor gave me antibiotics to be used ONLY if I developed a "secondary infection." The flu is gone, but my nose is now runny, I have pressure on the sides of my nose, my temples and neck ache, and I'm sneezing. I still have a lingering cough and some discolored mucus. Do you think this is a now a sinus/secondary infection? Should I take the antibiotics?