The heading should be read as "19 Years chronic pain in testicle"
Hi there!
Slight discrepancy in the size of the two testicles is normal and should not be anything to worry about. With infections/ inflammations ruled out possible causes of the pain that may need to be considered include trauma/ injuries, neuro-muscular causes, referred pain from other regions etc. I would suggest getting this evaluated by an internist initially and depending on the cause diagnosed/ suspected, it can be managed accordingly or specialist care may be sought.
Hope this is helpful.
Take care!