Son getting enough formula

My son is almost 4 months old. He’s starting to sleep 10-12 hours at night and I’m worried about him eating enough during the day to compensate. He’s formula fed.

Right now, he’s having 5oz five times a day so 25 oz total. But even then I’m almost forcing him to eat every 3 hours to make sure he gets all his ounces. (With my first I didn’t wake her to eat and she was an amazing sleeper too and she started losing weight so I’m worried about it)

But sometimes I try feeding him after 3 hours and he doesn’t act hungry but I’m worried he won’t get enough ounces during the day.

Should I let him eat when he’s hungry but try feeding him more ounces at a time? What would you do?

I’m nervous because with my 1st I let her sleep (she slept a lot) and it ended with us having to go to a nutritionist to get on a feeding schedule for her weight loss.

My son is about 12-13 pounds right now. He was very tiny at birth.