My mother tells anyone who will listen that I had a lot of beautiful brown hair until about 1 year old. Then all my hair fell out and it came back in later, thinner and blonde. I was a perfectly healthy child, so I would say unless agitation, pain, or unusual behavior comes with the hair loss that everything is fine.
I've never heard that a baby produces hormones that are related to breast-feeding so I wouldn't consider that a concern. If you still feel concerned, the best thing to do is talk to your doctor. It may seem like you are being silly, but there is no such thing as a silly question when it comes to the health of your baby.