Help please!!! Baby weight and height

So my lo had his check up recently and his doc said his weight and height hasn’t changed in about 2 months. He weighs around 19 pounds and is on the low percentile for height for boys at his age. Doc said he’d just keep an eye on that but other than that he’s doing well. But I’m just freaking out now and wondering what the heck is going on why is he not growing and gaining weight. He gets fed every 3-4 hours around 8 ounces per serving and he is fed solids 3 times a day. He doesn’t eat all of the food he gets but I try and have his eat everything since he’s blw he plays with the food a bit and likes to feel everything but it’s not like he’s not eating any of it....mamas any idea or has anyone gone through this?