What are the most common causes of testicular discomfort in men?

What are the different medical conditions or factors that can cause testicular discomfort in men, and how common are each of these causes?

Testicular discomfort can be caused by infections, varicoceles, nerve-related pain, or even kidney stones referring pain downward. My doctor said infections are among the more common reasons. I reached the clinic after searching online and was relieved it wasn’t anything serious.