Thanks for posting your query.
I can understand your concern because the symptoms of testicle pain, pain after urination and stomach tightness have been present since one year.
You have got most of the causes of testicular pain i.e. injury, STD’s, infection (Epididymitis or Orchitis) or inflammation, testicular torsion and kidney or ureteric stones ruled out. However in view of the symptoms one important possibility which I feel needs to be ruled out is of chronic prostatitis.
It is characterized by pelvic or perineal pain without evidence of urinary tract infection and persists for more than three months. Pain can be present in the perineum, lower abdomen, testicles, tip of penis, pubic or bladder area and there may be pain after urination and ejaculation.
The cause is not completely known but may vary from psychological factors to dysfunction in the immune, neurological and endocrine systems. Since it is a poorly understood condition, examination of the expressed prostate secretion especially presence of anti-inflammatory cytokine TGFβ1 and pro-inflammatory cytokine IFN-γ and nerve growth factor may confirm the diagnosis. You should discuss this possibility with your urologist.
There is no specific treatment but it includes a combination of medical therapy with antidepressants, psychological therapy and physical therapy(trigger point release therapy on pelvic floor and abdominal muscles, and yoga-type exercises with the aim of relaxing pelvic floor and abdominal muscles).
You have already taken two courses of antibiotics. You can take a longer course of azithromycin after prescription but it is not particularly useful for chronic bacterial prostatitis. Diagnosis needs to be made first and then specific treatment started. Taking antibiotics without diagnosis is just like throwing arrows in the dark without seeing the target.
Another possibility which should be ruled out is of a hernia without a bulge. In some cases, there is no visible bulge present, but rather mild pain in the groin area characterized by aching or burning sensations. This pain can cause referred pain in testicles or penis. Since you are having lower abdominal pain as well, it is better to get an ultrasound or CT scan of the area to rule it out.
Hope that this information helps and hope that you will get better soon.
Wishing you good health.