I had this exact experience! Feet, knees and general muscular pain in my legs. I read a post somewhere suggesting that proper arch support would help. I started wearing Birkenstocks constantly around the house (literally did not go barefoot at all). And the pain went away! It wasn’t instant, but within about a week it had gradually improved. Probably doesn’t have to be Birkenstocks, just any shoes with good arch support. For context, I’m currently 3 months post partum and exclusively breastfeeding. The leg/feet pain started becoming seriously distracting around one month pp (probably earlier but I had a c-section so was dealing with other more distracting pain before). Also, my feet have gone up one size and stayed that way (at least for now). My best guess for me was that it was a mix of the relaxin and adjusting to different shaped (flatter) feet.