Well- my first question is "do you primarily feed breast milk or formula?" Formula is a LOT heavier and should fill him up for longer periods of time than breast milk. If it is formula, I would begin to offer an ounce less every few night over the next 2-3 weeks until the dream feed is gone. If it is primarily breast milk, I would wait to cut the dream feeding until he no longer wakes 4 hours later for an additional feeding.
It typically get's a bit better once they are getting about 50% of the nutrition from food. Also- once he is eating rice cereal, feed him a good amount before putting him to bed. The rice will keep him full much longer than milk alone.
You're doing great! You boy is lucky to have such a great mama!