The lump which started off as a small pimple can be a boil, a hair follicle infection, a localized abscess, a hematoma or collection of blood or even a contusion. It is difficult to comment on the exact diagnosis. However, if it is not painful any more then probably there is no infective pus in it. With time such lumps usually disappear. Please do not touch it or puncture it. Show this to a doctor for confirmed diagnosis and further treatment if required.
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.