PIP like a mother!

Had my first injection of test e 250 mg in the right glute and thought all was fine and dandy. No pain during the injection and a bit sore the day after. 2 days after the right buttock has swollen and grown very stiff and tender to the touch. There is discomfort while walking and sitting down requires me to ease into it like no other. The pain is VERY uncomfortable. Whenever I sit down the pain will eventually subside so that I can sit on that butt cheek. The swelling is about the size of a grapefruit. This is day 5 since the injection. What could this be?

PIP like a mother!