One sided pain is very unlikely to be a yeast infection.
Common causes of one-sided nipple or breast pain include:
- Nipple trauma from a shallow latch, clamping, pinching of the nipple
- Nipple wound, crack, scab
- Inflamed duct / Bleb / Milk Blister
- Plugged duct
- Mastitis
- Vascular spasm (more commonly bilateral)
Click any of the above for details.