15 weeks postpartum sore knees?

Brittany
I noticed in the last 3-4 weeks my knees have been very very sore. However, I walk 4 miles everyday now with my son attached to me in a carrier. I always have walked this much pre and post pregnancy. So I'm not sure if it's walking with extra weight, hormones or both. Checking with you ladies to see if others are experienceing knee soreness.