Without a photo it is difficult to answer your question. However a small hematoma can occur (like a bruise under the skin) after any type of injection and this may be the case. I would recommend watching it and if it does not resolve in a few days, you should speak with your injector. A small hematoma can occur and is not uncommon with injections and typically resolves on its own in a few days.Best wishes.
It is hard to tell without seeing you in person, but this sounds like you may have developed a bruise, or hematoma, at the site of an injection. If the bump is stable, I recommend gentle massage and warm compresses, which can help to resolve this more quickly. If the bump is still growing, I recommend cold compresses to minimize the further bruising. If you have any concerns, I recommend calling the treating physicians office for further direction. While this is uncommon, this can happen with any type of injection. I hope this helps, and good luck! Sincerely, Dr. Daniel Jensen, Castle Rock Colorado