I checked the link you posted in your last response, and my thoughts are these.
There could be many reasons for the problems, including poor posture during the day and then when lying down in bed, the muscles are pulled. After several hours, pain begins.
Whenever there is back pain that continues without an explanation, it should be evaluated by a spine specialist.
Many times, simple things like learning good posture, and core muscle strengthening will correct a problem.
Without evaluation from a spine specialist, there is no way of knowing what is and isn't going on.
Fran