If you have anything happen after injections that you are worried about, it's always best to see your injector. While you could be describing a simple bruise, it's hard to comment on without seeing you in person or having a photo to look at. So it's best to call your injector and be seen.
"This answer has been solicited without seeing this patient and cannot be held as true medical advice, but only opinion. Seek in-person treatment with a trained medical professional for appropriate care."