No its because of the hardness of the injection u should rub the place firmly and dont press it hard u will get better soon .. but unfortunately if u could not find comfort than u should go to the doctor again for the check up
She could have definitely hit a nerve and wow, does that ever hurt.
If this just happened, try putting some ice on the area, that might help some.
It's normal for something like this to happen because Morphine and Phenergan make the muscle twitch slightly as side-effects. Check with a heart and immune system doctor for a layout and idea tracking of the pain if you are too concerned. It works for 90%-100% of the time.