I doubt your problem stems from the blow to your testicle. If you had severed your vas deferens (the tube that carries sperm from the testicle to the urethra, it would almost certainly have shown up on the ultrasound.
It's possible that since you were out of commission for a while you're pc muscles (pubococcigeal) got a little weaker. Have you tried Kegels? These are exercises to strengthen the pelvic muslces - and they are a part of ejaculation. Google kegel exercises, and try them. Maybe it will help. PS why is having a large volume of ejaculate important, anyway? It just makes more mess. If it feels good, that's what matters. Don't compare yourself to the porn stars. They take all kinds of drugs and have way too much sex. Good luck.
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