Not really long term, but I was in Hospital for 5 days a few years ago with severe abdominal pain (Turned out to be duedonitis). I needed morphine just to be able to sit still and they would come round and fob me off with paracetamol even though I was clearly unable to eat or sleep due to the pain. The single worst 5 days of my life... the final straw being a wander around the hospital at 2am, whilst wheeling my empty drip, looking for a nurse so I could beg them for some water.
I am genuinely psychologically scarred from the experience.
I'm guessing proper pain killers are expensive which is why they don't hand them out readily. Luckily they gave me some tramadol when the discharged me, but I had to wait 8 hours for the pharmacy to bring them as they tried sending me home with some paracetamol...
I hope you get sorted out mate, there's nothing worse than being in pain and people not taking you seriously or wanting to help. I now pay for Bupa, such is my fear of having to go back on the NHS.