Nerve damage (diabetic)

Hi all i have had severe nerve damage in both legs since 31st March this year. I was off work for 3 months and had a very low mood which for me is unusual. Initially i had been prescribed a range of drugs to ease the pain. It was first thought it was diabetic neuropathy which my diabetic team don't think it is. As the pain has not presented itself in the usual way. They said the nerve pain usually starts from the feet and works up the legs. I have had no pain in my feet atall. I have had numerous tests, tons of blood taken, MRIs, electrical impulse tests, camera down my throat. Yet still no diagnosis, unfortunately the NHS is in a mess as we know but until now i hadnt realised how bad. But when your told there is a 25 week waiting list for an appointment to see a neurologist and a letter through the post for pain management for mid September just gone, baring in mind this is from March this year. Anyway the pain at its worst gave me suicidal thoughts i swear it was horendous. I am on 150mg Pregabalin a day and 400mg Tramadol for the nerve pain. Since June 24th ive been on this regime and if this combination had not worked for the pain god knows where i would be. It was like a miracle within 2 hours of taking the Tramadol the nerve pain about dissapeared by around 70% it was amazing. That is where i am today with no more forward on diagnosis just being managed by the tablets. My GP did not want me on Tramadol for this long but it has been a life saver literally and i promise you i am not making this up. Does anyone have any ideas what would cause this nerve damage to start? It came on like i said 31st March with no warnings and no medical proffessio als can give me a diagnosis. Help required or information and guidance if you have some. Regards Chris.
Sorry for waffling on.