I think Hallamshire is on the money here with a neural interpretation of this long standing problem. The most common cause of pains like these are to be found in the Lumbar spine, specifically at L3. Ongoing protective behaviour in the mid lumbar spine may or may not have it's origins in childbirth , but may persist for many years. Not uncommon also is a state of referred pain that is not matched by pains local to these irritations in the low back. I often see those for whom the only signal is a refered pain. Sounds like you would benefit from finding a physiotherapist with good hands who is capable of mobilising spinal joints. Manipulation or massage will be unlikely to be helpfull.