Based on it information provide it seem like "HEMATOMA" caused by blunt trauma
BLUNT TRAUMA - can lead to a collection of blood pooling inside the organ known as "hematoma", it may not be visible by naked eyes but may be hidden deeply ( the shock
wave can create an tiny blood vessels to rupture leading a loss on blood internally in the organ but the cover of the organ will mostly enclosed it so it will not come out but will stay their) eventually it will be healed by absorption and macrophages(blood cell) will engulf the hardened dark blood but will take a long time to regress.
Please take an medical attention, and reasons of it are as follows
1) The pain still their and getting worst.
2) Their are chances of getting it infected.
3) May need ULTRASOUND
to access any other deep injury
Treatment mostly include
a) Pain killer,
b) Antibiotic in case of infection is suspected.
Hope it helps.