You could check with your vet to make sure he's normal for his body type. My Joel is the same way he's 7 1/2 lbs but he's taller and skinny looking, and if it wasn't for his afro hair you would think i'm starving him, lol he's also very boney. I can feel all the bones from his spine. But he eats alot so for him thats just his body type. Thats probably how your baby is