Daughter not gaining enough weight

So i had gave birth to my daughter almost 3 weeks ago on Saturday she weighted 5lbs 15 oz at birth carried her 40weeks and 1 day (December 23rd) had her first doctors appointment on the second of January she weighted 6lbs 4 oz and as of today at the doctors she weights 6lbs 8oz and doctors said she’s not gaining enough weight..Anyways i can help other then breast milk as i do not produce a lot and she will not latch on..currently she is on formula (Enfamil w/ iron)