Self weaning at 13 months?

My LO was happily nursing in the morning and before bed and one morning woke up and just started refusing the breast. The way he made a face at it made me think perhaps something changed with my milk. I'm definitely not pregnant and he will take my milk expressed from a cup or bottle. I've kept offering but no pressure. He turns his head to the side and makes a face like no thanks. I've heard that child-led weaning happens slowly rather than all at once so I'm a bit surprised. Happy to follow his lead, but wanting to rule out teething. Has anyone else had this happen?