Falling off growth curve

Ok so my son is 4 months old. Nurses like a champ. Plenty of wet/dirty diapers, plenty of milk, no ties, no latch issues. But he has almost stopped in growth.

Jan 5 he was 14.7 lbs, Jan 28 he was only 14.13 and has not grown in height or head circumference. He is almost falling completely off the curve and the pediatrician is a little concerned. The doctor mentioned fattening up my milk more, that he may just need some extra calories.

Has anybody had to do that and it be successful? I really do not want to have to give him fortified breastmilk 😭