1. Lie on your back. ...
2. Cross your right leg over your left so that your right ankle rests on your left knee.
3. Use your hands to grab hold of your left knee and pull it gently toward the opposite shoulder. ...
4. Hold for 15 to 30 seconds.
5. Relax, and then repeat with the other leg.
6. Repeat this cycle 2 to 4 times.
Back ache can arise due to multiple causes including back posture, low vitamin D, infection or even disc prolapse. Do get basic investigations like calcium, phosphorus, alkaline phosphatase , vitamin D levels, uric acid, CBC with ESR. Also get x-ray LS spine AP and Lateral views and see an orthopaedic surgeon in your area.