Hi thanks for your question.
The bump you are complaining of following head injury
most could be haematoma (collection of blood under skin and muscle) .The haematoma will disappear of itself slowly with out any treatment unless get infected.Your main problem is pain, for which you can take analgesic
anti inflammatory drugs(pain killer) like ibuprofen
. These drugs besides reliving pain will also help in resolving haematoma.
Hope this answers your question.