Did you remove too many headset washers? perhaps you don't have enough stack height to prevent the top cap from bottoming out against the steerer tube. You need to be about 2 - 3mm above the steerer before tightening the top cap.

If you have clearance, turn the front fork sideways and rock the main frame of the bike forward and back and check for play. If loose, check the front hub. Is the QR tightened? Check the brakes themselves; do they have play? And check front hub bearings to see if the hub has play.