I think Genevieve has hit it on the head. The injection into the carpal tunnel always risks hitting a nerve, as the median nerve passes through the same space, with the inflamed tendons.

Certainly tylenol or better, ibuprofen, might help ease it a bit. You could try icing it, too.

If it's still bad after 24 hours, I'd get it looked at by a doctor, soon.

Lar