Weight gain question IUGR baby

Hey mamas. Did any of your babies experience a drop in their weight gain when they changed from formula to solids and whole milk? My little guy is 15 months old (12 adjusted) born weighing 1lb and has been gaining about 1lb a month but that’s slowed this past month which is also when we switched off formula. I’m making him 3 meals a day and giving him tons of snacks but as I’m sure you know most of it goes on the floor or to the dog lol.