Not enough weight gain? Formula fed

angel • 👶🌈🌈👶🤱

My baby is 7 week's today. She spits up once or twice a day but it's about an ounce. She'll take 4 oz maybe twice a day and the rest its like 3-3.5 . Every 3.5-4 hours. She's only 9.4 lbs was born at 7.7 i jessup seeing pics of all these chubby littles and she's still in newborn clothes. She Been sick the last week and a half with a gross cold and i don't know if the post nasal drip is effecting her. Drs keep saying she'll catch up but she's in like the 16th percentile and I'm nervous. My boys eye eating 5-6 ,oz bottles and wearing 3 months clothes by now. Advice please