Greetings,
Sorry about your pain. Your back muscles are not supported by abdominal muscles just because back muscles are stiff and long. When I say back muscles it includes hamstrings, calf, so stretch them. there are other muscles which a therapist can assist by examining you. This is not serious issue, just muscle imbalance. If you have any other symptoms please do mention so that I can broaden by view.
Next Steps
See a physio with the above in mind. they will assist you.
Health Tips
ice your back muscles for 5 to 10 min twice a day or as needed. place pillow between thigh when sleeping in side lying position