If you have seen someone good for assessment and they haven't been able to pick up anything obvious on examination, and you have tried time (watchful waiting) and exercise, then it sounds like you probably do need further investigation in terms of x-ray/MRI. This can then hopefully pick up anything structural that may be going on. Otherwise, it's really a guessing game, and if there is nothing obvious, then it's not a very good guess either! Hope that helps.