Any mommas have a baby who is/was labeled as “failure to thrive”? My 4 month old is 13 pounds even.…

Any mommas have a baby who is/was labeled as “failure to thrive”? My 4 month old is 13 pounds even. He was born 7 pounds, 9 ounces. He lost almost a pound when I was breastfeeding him. I wasn’t getting enough milk. Then we switched to formula but discovered he had a milk protein allergy. Then he got sick with an infection. So I know all that probably affected his weight. For the past month/month and a half he’s been drinking formula with an extra scoop (recommended by his doctor) and rice cereal in a couple of bottles a day so he can get extra calories. Within the past month he’s only gained 6 ounces. He’s in the 7th percentile for weight. She now wants me to spoon feed him baby food veggies. She doesn’t think there’s an underlying medical condition causing this, but I’m honestly not too sure. Don’t you mommas think he should be gaining an adequate amount of weight given he’s taking in an extra scoop of formula every bottle and rice cereal? My first has always been chubby, like crazy chubby. So I’m not used to this and never been through this. I’m just starting to get worried....