Sleeping too much?

My son is almost 3 months old. We switched him to soy formula a few weeks ago and since then he’s been sleep a lot more than he was in the hospital. Could there be something wrong? He’s always slept through most of the night, but now he’s when from 8 hours a night to 14 with one or two feeding. I’ve tried waking him up after the recommended four hours but he will refuse to eat or eats very little. He’s also been sleeping more during the day at least four hours or more. He’ll eat anywhere between 2.5-6oz with maybe five feedings. A lot of the time he will refuse to eat early. He’s dropped two growth curves and is underweight with his length. I’m seeing the dr in a few days for a weight check, and will mention it to her of course but has anyone else had this? Is this just normal? He’s very active and happy when he’s awake and developing faster than most babies his age. I’m just worried because he’s sleeping more and eating less than what he was when he was born. Any suggestions on what I can do to keep him up long enough to get a full feeding in or wake him up at all? He sleeps through most of his diaper changes, touching, talking and moving around don’t work either.