My 2 month old son has thrush for the third time in the last 2 1/2 months, why does this keep recurring?

2nd opinion. Recurring thrush in an infant can be a sign many things that should be evaluated. If you are not finding relief with your current pediatrician, i would seek a second opinion. Rarely, this problem can be a function of immune system dysfunction. Good luck to you.
Thrush remedies. Are you breast or bottle feeding? If you are bottle feeding make sure you wash and sterilize bottles. If you are breast feeding make sure you wash your breasts before and after feeding. You may also want to apply an anti fungal medication to your nipples. Lastly it sometime takes a while to get rid of thrush despite your best measures.