Our old doc gave us antibiotics for colds and we got better. Why don't you?

Don't work for colds. Colds are viral infections andnot treatable by antibiotics. Many physicians still prescribe them incorrectly due to several reasons; uneducated decisions, pressure from parents, or trying to please parents. Regardless, antibiotics should not be used for colds as they are ineffective and unnecessary. Improper use of antibiotics has lead to bacteria that now cannot be killed due to overuse of abx.
They don't help. You'll get better from a cold in the exact same time with or without an antibiotic. Your body's immune system does the work, not an antibiotic which has absolutely no effect when you have a cold. (well, the antibiotic could give you diarrhea or help you develop an infection from MRSA or one of the other "super bugs", but i'm guessing you don't really want any of that!) fluids, rest, chicken soup!