I'm surprised your doctor called in an antibiotic to take care of a cold! Shame on him! They don't work on COLDS (otherwise we'd all take them every time we got one, right?).
Now, I can see taking antibiotics to make sure you don't have some other infection (as an "insurance policy" per se) but not for a cold. In fact, my doctor took some blood tests and said that if there was some sort of infection present (or proof of prior infection) in my body that I would be given antibiotics during delivery -- but it turns out I don't have whatever that was, so I don't need the prophylactic antibiotics after all.
The danger in taking too many antibiotics is that your body can build up an immunity to them and then the bug mutates to get around the antibiotics, and can cause some potentially dangerous infections. I had taken lots of antibiotics for chronic sinus infections over a few years... now I can't get a sinus infection to respond to anything but Avelox or Augmentin, both "heavy hitters" in the antibiotic world and that cause major digestive problems.
I hope you feel better, though... and that your c-section goes fine!