It seems that you may be having post traumatic ecchymoses and swelling on buttock.
It may be hematoma
or sot tissue swelling.
Take bed rest
compresses might reduce swelling.
Take anti inflammatory drugs, serratopeptidase ,vitamin C and antibiotics for 2 weeks.
If there is erosion , apply antibiotic cream.
If there is only bruise
, apply thrombophob oint.
You may be improved, still, you consult surgeon.
I hope you got my answer.
Dr. Ilyas Patel MD