baby fell under average percentile chart

Jennifer
So at night it is so hard for my baby to wake up and eat. He is extremely lazy & just wants to sleep. Yesterday was his 2 month check up and he only gained 1 pound since his first month check up which made him fall under average. I try to wake him up every 3 hours to eat, but he will just not eat until the 6th hour. Any recommendations on how to help him?