While bruising does not typically happen with an ear piercing, it is possible. Give it the normal healing time of 6-8 weeks, and take care of it as directed.
This issue you are having is completely normal. When you get your ears pierced it always seems kind of sore for a time period which can seem longer than normal. The bruising could have happened if you bruise easily or just from the gun they use to do the piercing.
This is not that unusual; they probably hit a little blood vein. It should go away within the next week, just don't press or pick on it and keep it clean.
I wouldn't worry about it unless the pain increases or the bruise doesn't fade in a few days. A little bit of discoloration and tenderness is normal for the first few days after getting a new piercing. Try applying some properly insulated ice for a few minutes at a time.