It can be easy to stuff your purse or backpack with a lot of stuff, but this can make your bag heavy which can cause back pain. Carrying a heavy backpack causes an uneven distribution of weight that puts strain on your back muscles and causes pain. Carrying heavy bags for long periods of time can cause you to have poor posture. Try to keep your backpack or purse as light as you can to avoid any pain. If you have to have a lot of stuff in your bag, try switching the bag from arm to arm to avoid any strain.