I've noticed a white ball in the entrance of my vagina probably a nickel size, no pain but what can this be?

Most likely a cyst: Depending on the exact location, it may be a bartholins gland cyst, skene (paraurethral) gland cyst, urethral diverticulum, less likely a urethral caruncle, inclusion cyst, skin tags, remnants of the hymen, etc. If it bothers you, then see your doctor for a diagnosis and possible removal. If it becomes painful, then it's most likely is a cyst that became infected with abscess formation.