Acting hungry but won’t eat?

My 15 week old used to eat 4-5 ounce bottles every 4-5 hours. Now the max he’ll do is 4 but the past 5 days it’s rare basically takes 1-3 ounce every time he eats which has become every hour and a half to 2. He keeps rooting but everytime I go to feed him he bites the bottle or turns his head continuously. What in the world is going on? My older 2 were never this complex.