I think 25-32oz at only 3 weeks old is an awful lot. Their tummies are still very tiny, and that's a lot to take in! I'm not a doctor either, but I think either way--bottle, or breastfed, you should feed on demand. When the baby acts hungry, feed him/her however much they want to eat! If the baby has any health concerns, or if you feel like he/she isn't eating enough then definitely talk to your doctor about it, but in general, babies know just how much they need. I think people are much too caught up in measuring the amount a baby needs to take in if he/she is bottle fed. You never know how much milk they're taking from the breast (unless the baby is weighed before and after a feeding with a very sensitive infant's scale), but it's usually enough!
If you're concerned definitely talk to your dr.
Whiskers