What Does Hard, Small, Painful Lump On The Bottom Of Testicle Suggest?

I have a small lump like symptom on the bottom of my right testicle and it hurts if I apply a little pressure. And other days the whole right testi may become entirely fragile where it hurts to move. I have also noticed it can become rock hard and feels a if it's a different shape, this happens after certain activitys. What is this