Neck exercises that do not put the head into extension. Make a U with your chin 10 times slowly. Then make an X, looking from you right shoulder up to the left and then from the left shoulder up to the right. Do these to make 10 'X' s. Do these in sets 2x/day. Then push against your hand providing resistance while doing the X maneuver for 5 X maneuvers. Do these regularly and see a chiropractor if the new bike fit doesn't completely clear up the problem. If it returns the problem is usually simple, Don't put it off because these things get more complex the longer you 'live around it'.
I am a chiropractor!