birth control and antibiotics

Hi guys- hate to post but feel like I need to collect opinions!
Was treated for a yeast infection, and a week later had sex (without backup). 
My doctor never told me that this may decrease the effectiveness of my birth control. 
Obviously now I have reason for concern.
Thoughts? I've never missed a dose and have been on my pill for over three years. 
Appreciate any feedback! Thanks ladies!