Check to make sure this is not right at the valve stem. When replacing a flat if you don't manage to get the tube all the way into the tire then you can get a bulge like that. So make sure the tube is in the tire securely and straight before you attach it back to the rim. Try swapping tubes between your front and back tires if to see if it is a tube problem... if you still get the same outcome with the same tire then the tire wall is failing and you're gonna need a new tire. Could you post a side shot of the tire bulge as well?