I have had a small growth on my testicles for quite some time now, and i popped it recently, puss came out. now it's back and harder than before.

Epidermoid Cyst: What you have described on your scrotum is an epidermoid cyst. These are common and usually remain without symptoms. Thus they don't need treatment. However, you describe an infected cyst with pus. After the pus passes, there will be hardening of the skin which will resolve. These cysts can be removed but if the entire cyst wall isn't taken, they will recur. See your doctor if infection returns.