That's odd, it's hard to know why our bodies do what they do sometimes!

What position are your legs in when you feed DS2? I had mystery ankle pain when DD was a newborn and couldn't work out why until one day it clicked that I was sitting cross-legged when feeding and lifting my "grounded" foot up by my toes (ITMS?) which was causing a kind of repetitive strain injury. I was doing it unconsciously and it took a while to work it out LOL!