Hi, so sorry that you're going through this! Fellow Brit here struggling with constant pain on all my joints for 5+ years that have been dismissed by NHS several times. I fed up and went to a Rheumatology Clinic in Turkey last October, got diagnosed there, came back and showed all the results including the MRIs, Xrays, diagnosis and the prescription. Just in December saw a specialist reffered by my GP, he diagnosed me with seronegative arthritis, prescibed sulfasalazine, which I see minor improvement and some days it still flares up to be unbearable.
Hope you'll find the help you need in no time, keep on fighting!