How long after taking antibiotics should I start taking a yeast infection medicine?

Prevent it. If you are not having yeast infection symptoms do not take a medicine for it. It you know you get them after antibiotics prevent them. Take probiotics while you take antibiotics (separate by several hours or antibiotic kills probiotics) and for a month afterwards. Eat more alkaline foods like cucumbers, avocado, and celery as it helps prevent infections on general.