Welcome to Healthcare Magic,
Yes, your bruises can last for few weeks, antibiotics you need just as a prophylaxis to prevent any infections. Regarding this lump , in your case is suggestive for hematoma
that occurs frequently after blunt trauma
on soft tissues and normally will subside as well within week or two, but if you will note this lump increased in dimension with pain, high local temperature, changes in skin color then you must go asap to your Physician for reevaluation.
I wish you good luck and speedy recovery.
Hope this helps and I have answered your query. If you have additional queries don’t hesitate to ask.