Chronic testes pain, back pain and lower abdominal pain is usually related to noninflammatory conditions but chronic infections also should be considered. Because the testes arise embryologically in close proximity to the kidneys, pain arising in the kidneys or retroperitoneum may also be referred to the testes. So an abdominal ultrasound, intravenous pyelography and a CT scan of the abdomen should be done to evaluate testicular pain.
A urine and sperm culture for pyogenic organisms and mycobacterium would also be advisable. This should be able to point towards the chronic infection and give the guidelines for the further management.
Following other causes to be considered for the pain in your case are;
1) Recurrent torsion
2) Torsion or inflammation of the appendix of the testes
3) Infectious epididymitis
4) Noninfectious epididymitis; occur due to reflux of urine through the ejaculatory ducts and vas into the epididymis, producing a "chemical" inflammation
5) Referred pain - the genitofemoral, ilioinguinal, or posterior scrotal nerves CAN CAUSE REFERRED PAIN. Other causes of referred pain are abdominal aortic aneurysm, ureteric stone, lower lumbar or sacral nerve root impingement, retrocecal appendicitis and retroperitoneal tumor.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.