You had a hit 2 weeks back, now only a bump is remaining with the size of a grape fruit. It may be cellulitis
, abscess - but both these conditions are painful.
It may be a Hematoma
and may not be painful so long is not infected.
Abscess or hematoma needs an adequate incision and Drainage
with a Pack and every day dressing to prevent collections, along with antibiotic and anti inflammatory drugs.
As you say the bump is hard - better to take X-ray to rule out fracture