My Aching Back

Yesterday, while reaching down to grab a onsie for Sully, I pulled my lower back. How is it possible for me to move furniture, lug pounds and pounds and pounds of laundry up and down two flights of stairs, carry around an 18 pound baby, etc. and yet pull my back while picking up a onsie???? I'm sure much of my back issues can be attributed to my weight. Weak stomach muscles make for weak backs. I've lost just about five pounds and am trying to recover from a weekend of not sticking with the healthiest of eating. Weekends really are my hardest time.