Take a pH reading of the finished beer at room temperature. It should be in the 4.1 to 4.5 range. Too high and it can taste dull. Too low and it can taste thin, and start tasting sour.
But, yeah, we need some more details to give you specific help. Do you have any local judges or experienced brewers that can help you identify the flavors? There are a lot of different things to try, but it would help if we can narrow it down first.