baby eating less and sleeping more

Anna

My 12 week old baby (14 pounds) used to eat 5 oz every 3 hours but for the past week he has been barely eating 3oz every 3-4 hours and he is sleeping a lot during the day and sleeping from 8 to 5 during the night. I really don’t know what to do in a total of 24 hours he is eating almost half of what he ate before and sleeping for long naps 2-3 hours while before he barely slept for 45 minutes in his morning naps