Hydrocele/varicocele

'A soft lump in the scrotum, especially if you can get your fingers between it and the testicle, is most likely to be a hydrocele. This is a collection of sterile fluid in the cord attached to the testicle, which is invariably harmless. Left untreated, a hydrocele can grow to a large size and cause discomfort, so they are usually best drained early.

Varicoceles are similar, except they are caused by enlarged blood vessels. Both may require surgical removal in severe cases.

Neither condition is dangerous except in very rare cases when they become infected or put pressure on blood vessels.'

So it seems that the only bad thing about what you have is that is' quite painful, just get it drained at the docs.