Ultrasound shows moderately atrophic testicle with diffusely heterogeneous echotexture and minimal blood flow within the superior aspect.presented with pain in testicle 4 months after varicocelectomy, and nausea. what could be wrong?

Vascular Compromise?: It might be possible that the arterial supply to the testicle has become compromised. An abrupt interruption in the blood supply would cause severe acute testicular pain, often with swelling. If the vascular supply was partially compromised there could be intermittent pain and shrinkage. A more detailed doppler study of the testicles could provide more information about vascular status.

Lack of blood flow: Sounds like you could have a loss of blood flow due to your varicocele ligation discuss with doctor or get 2nd opinion.

Varicocele: Atrophy of the testicle can cause testicular pain and tenderness. The varicocele repair might have damaged the vascular supply of your testicle. A comparison of a testicular u/s before the surgery if one was done, could help explain if the atrophy was already present or not. Varicoceles are known to cause atrophy.