Hi Will,
You posted some time ago, so not sure if you are still suffering - I hope not. However, if you are, sounds like you need some support to help you understand and take responsibility for helping yourself to heal.
I'd suggest 1:1 pilates, from a fully qualified Pilates Foundation teacher. You can find them on the Pilates Foundation website, and see which teachers work near to you. (Hi Moderator - not advertising, this is genuinely my advice and I'm trying to help)
Or, alternatively, Google to find a good Scaravelli Inspired yoga teacher nearby. They specialise in working with the spine and freeing up the vertebrae. My teacher (John Stirk - an osteopath and yoga teacher) has had two herniated discs, and now moves with absolute freedom - you'd never know he was confined to bed for 6 months. He now teaches mostly teachers, in West London, but there are several of his students scattered around London, and you could possibly find one of them to help you. Obviously, if you have a disc problem, you will need to take medical advice before embarking on any physical exercise plan. Pain down the outside of the leg is a pretty classic symptom of sciatica (inflammation/irritation of sciatic nerve - possibly from bulging disc, sometimes from tight piriformis). This will be aggravated by sitting a lot and little physical movement.
From your posts, it sounds like you need individual attention, which will be around £60 per hour, but should help you to get back some control. Gradually, you will be able to move back into class situations, and then keep up the exercise. If therapists or teachers behaviour is confusing, then you could ask them about it - they should be able to justify their reasons for giving a short treatment, and I would have thought they should charge you less for it. It seems only fair and reasonable.
I hope this helps, and that you get better soon.