Ive had dull pain in the middle left side of my back for some time. never a big issue. no blood anywhere and no other issues. had 1 beer late in evening last night, the pain today is worse and hung over like crazy. also feel constant need to poo?

There a various causes of that type of pain. Among them are musculoskeletal & kidney causes. You've never seen blood in your urine, but I recommend having a clean catch urinalysis with a microscopic examination of the urine sediment to look for red blood cells which would indicate possible urinary tract pathology. Xrays of your lumbosacral & thoracic spine is a good screening test also. See yourMD