3mo old after returning to work

My baby was a really good sleeper and going 3-4 hours between feedings prior to my returning to work 2 weeks ago. Now, he eats every 1.5/2 hrs after work and is up every 2 hours at night!? He used to sleep in 3-5 hour stretches at night. Is he not getting enough to eat at night that he's able to get full? Does he just miss nursing during the day? Should he really be hungry every 2 hours over night? Help!