I am a post-graduate spine specialist in the USA, certified by a group from your land. If you have not seen a certified McKenzie therapist(Mechanical Diagnosis & Treatment of the spine) I would seek one out. You can find them worldwide by going on their website McKenzieMDT.org, choose your country, & locale in that country.
My problem with what you relayed is that if the therapist doesn't know hat it is then I would have a hard time believing he knows what it isn't. Some discs do not respond to treatment even tho they are the culprit. A torn annulus will not respond.
- - - Updated - - -
There are too many questions to ask to f/u on your clues. If 1 movement abolishes Sx's temporarily then I would have you do many and see if it relieves it for prolonged periods or holding knees to chest for a period of time