Wa'alaikum assalam sis! Aww, that sounds uncomfortable! Kalau tapak kaki sakit macam tu 3 hari and it hurts when you walk, best you see your doctor or go to a clinic , especially since you're a new mum, banyak berdiri and carrying baby kan. Could be so many things (swelling, pressure, infection) and kena check properly je. A few of my mum friends ada yang experience foot pain masa postnatal and it turned out easy to fix once doctor checked, so don't suffer lah! Go get it looked at, okay? Take care!