Baby eating less?

Stacey • Mommy to a 1 year old🎀. Expecting #2 in January!
My little guy is 7 weeks. He still want to eat every 3-4 hours but when I go to feed him he only eats half of his bottle. He used to chug 4 oz and now it's hard to get him to finish 2. Is this normal, for his appetite to change like this?