Im 25 male i have a swollen left testicle with a small lump no pain just ache which comes and goes.what could it be?

Testicle mass: Go see doctor to check this out, testicular cancer is the most common cancer in man between the ages of 20-39, .

Get checked up: If you have a lump on your testicles, i strongly recommend you be checked by a doc. You're in the age group that has highest prevalence of malignancy of the testicles, so i would definitely get tested. There is a whole range of non-malignant conditions presenting the same way, but you cannot just shuffle them away without a work up.