You got a yeast infection from the antibiotics. It's very common.
You can get over the counter medicine for this, or otherwise tell your doctor, (call him/her) and tell her you got a yeast infection from the antibiotics. he can call in a pill that is only one pill to take, and works like magic. It's rather expensive, though. Or, he can also prescribe a cream. Don't worry. it's inconvenient but not serious. It's usually wort before your period.