Thanks for posting your query.
From description it seems soft tissue injury
over your butt.
I suggest you to consult an orthopaedician nearby for a detailed examination. You may get the X-ray of the area affected under his/her guidance .
In the interim,apply ice packs to the affected area,anti-inflammatory drug like motrin
to reduce pain and inflammation. Avoid putting weight and rest well.
Wishing you good health
Dr Saurabh Gupta