Failure to thrive???


So my son was born September 26th and he’s a pretty small baby. He’s slightly under 23inches and on the 5th percentile for height. He’s always been small but his percentiles keep dropping lower and lower. For his first month he was on the 17th, second month the 12th now he’s on the 5th! I am just concerned next month he will be on the 0th and considered “failure to thrive”. He is growing and gaining weight, and eats 5-6 ounces every 3 hours, but is still tiny. Both me and my husband are kind of on the smaller side (I’m 5’2 he’s 5’5). Does anyone else have a smaller baby? Should I be concerned with the percentile??