It is unlikely that the antibiotics your child took a month ago are causing the current symptoms. In this situation, it is best to monitor your child's overall condition, encourage them to drink plenty of fluids, and offer light foods such as soups, crackers, toast, eggs, etc. It is important to keep an eye on any rashes or redness, and if they worsen or persist for more than a week without improvement, it would be wise to consult a healthcare professional as a precaution.