my baby have the same problem when she is 1 month old, Doctor said to change milk powder to NanHa1 immediately (all meals to new one, no need to insert in many days). She is okay then - face back to normal & have stool everyday.
Two weeks later, she don't like the taste of NanHa1 & refuse to drink more - only 1 or 2 oz every meal, then we see doctor again & change to Wyeth S26 HA immediately (also to replace NanHa1 by new milk powder in every meals). She is okay & able to drink 5 oz in every meal.
According to doctor & my experiences, babies in this age (1 to 3 months old) are easy to adopt new milk powder & you are able to change immediately.