I Had Gestational Diabeties And My Baby Isn't Gaining Weight

Does anyone know what's normal to expect with weight gain after a baby has been born with gestational diabetes? My baby was born weighing in at 10lb,12oz due to my having gestational diabetes. Now, almost 4 weeks later she still hasn't gained back to birth weight, and infact lost 6 oz this week even though she eats great. Is this normal? My pediatrician doesn't seem to know.