You need to put some stress on your bones. That is why jumping up and down seems to work. Walking is great exercise, but doesn't add much stress. Add a weighted vest or walk with a bounce or skip. Just don't over do it. If you are jumping start slow with just 10. Start with 5-8 lbs weight. etc.
And , just what gently said. be careful of how you lift. Use your legs.!! Doing core exercises. A strong abdomen supports your back.
-1.1 is not bad, but probably good to get ahead of it.