Dude, just have it checked out to be sure by an MD. An urologist is what you need there.
It could be a gazillion things, some good, some bad. It could just be an inflamation of the seminal canal or it could be inguial hernia ( google them to read up on the subjects ).
Usually when looking for abnormalities on the testicles we learn to "watch out" for lumps in the testes, the more worriesome of them being the odd masses at the SIDES of the testicles. Rarelly they are found on the tips.
Does it hurt? Is it painless ? Why are you asking for medical opinion on here?
Get it check up NOW.
Infertility issues may or may not arise. The DOCTOR will tell you, not us net-mongering dudes that are here to get a bigger unit.
Sorry if i'm so blunt but you really need to take this matter to the one's that actually studied and experimented with this kind of stuff/issue.
Peace
Let us know how it went at the doctors office.
Mike