The problem with treating your cold with a round of antibiotics is this: Antibiotics are used to treat bacterial infections, but colds are not caused by bacteria. Colds are caused by viruses, more than two hundred varieties of them. Antibiotics won't help at all.
In fact, they may be harmful. Taking antibiotics when they aren't needed or helpful is adding to the growing problem of antibiotic-resistant bacteria, making it more difficult to treat you with antibiotics when you do indeed have a bacterial infection. They can also cause a host of unpleasant side effects, such as yeast infections and diarrhea.
Sometimes, other conditions look a lot like a common cold, at least at first, including ear infections, strep throat and pneumonia -- these are actually bacterial infections, and should be treated with antibiotics. Other times, bacterial infections, such as a sinus infection, may develop after a cold, so if your cold symptoms don't get better after about one week to 10 days, see your physician.