It is very possible that you have something called "epididimitus" that is an infection and swelling of the epididimus and can be easily treated with anti-biotics.
I have chronic problems with that and since they changed my treatment from e-mycian to tequin 400 I have not had a problem with this. (since december)
it very well could be something much worse like a "torsion" where the testicle twists inside the scrotum and cuts off the blood supply or even possibly testicular cancer.
When it comes to my tools, I go to the doctor asap! Pain down their can mean death and a very painful one at that!