Epididymitis: This is the most likely diagnosis given the patient's symptoms of testicular pain and swelling. Epididymitis is an inflammation of the epididymis, often caused by bacterial infection, and is common in sexually active men. The patient's history of diabetes (DM) may also increase the risk of infections.

Orchitis: Inflammation of one or both testicles, usually caused by bacterial or viral infections. It can present with testicular pain and swelling, similar to epididymitis.
Testicular Torsion: Although less likely given the duration of symptoms (two weeks), testicular torsion is a condition where the spermatic cord becomes twisted, cutting off the blood supply to the testicle. It typically presents with sudden, severe pain.
Hydrocele: An accumulation of fluid in the tunica vaginalis, a potential space around the testicle, which can cause swelling but usually not significant pain.

Testicular Cancer: Although rare, testicular cancer can present with a painless testicular mass or swelling. Given the potential for serious outcomes if missed, it's crucial to consider this diagnosis.
Acute Appendicitis (with an atypical presentation): In rare cases, appendicitis can present with testicular pain if the inflamed appendix is located near the testicle, causing referred pain.

Spermatocele: A cystic structure filled with sperm, which can cause swelling but is usually painless.
Varicocele: An enlargement of the veins within the scrotum, similar to varicose veins, which can cause a sensation of swelling or heaviness but is typically not painful.
Henoch-Schönlein Purpura (HSP): A form of vasculitis that can cause testicular pain and swelling, among other symptoms, but is relatively rare and usually associated with other systemic symptoms like purpura and joint pain.