What Is Causing Decline In The Body Weight Of My Daughter?

My daughter is now 2 months 10 days. She was weighing 3.25 kgs at birth, after 15 days it came down to 2.4 kgs. And now after 2months she weighs 3.3 kgs. My doctor has said the baby should gain approx 1 kg every month and going by that she seems underweight. She is getting totally breast feeding, but at times she is womitting. Doctor has prescribed digestive enzymes for increasing hunger. Kindly suggest if the weight is normal or if any further investigation or medicines are needed?