From what you report above:
It is NOT a torsion.
It is not an infection in the testicle (orchitis)
It is unlikely to be Epididymitis unless you have been sexual active with an infected woman.
It could be due to unusual and excessive muscular activity e.g running, lifting etc.
Like your other medical advisors I cannot come up with a definitive diagnosis but agree that an antibiotic and an analgesic e.g is the way forward.
Watch and wait.