3 week old baby eats 2.5oz of breast milk every 2-4 hrs, with 2-3 supplemental formula bottles included in her daily feedings. Is she eating enough?

Hard to say. If she's playful, interactive and starting to fill out it is likely enough.Having her weighed to see is also an option but once a week is often enough to monitor weight.Most at her age will put on at least an ounce a day.