Baby not gaining weight

We just got back from our 9 month appointment which is actually closer to 9.5 months because of Christmas and New Years. My baby has not gained any weight since his 6 month appointment. Since that appointment we have started solids - he eats table foods in fairly generous portions. He is also breastfed. He is hitting all of his milestones. Has anyone else experienced this? Our ped was a bit concerned as he has obviously dropped from his curve and generally confused about how he could be the exact same weight and we are going to go in for a weight check in a month.