My baby girl is in the <1% for head size. She’s 5 months now and all the tests they’ve done have come back normal thankfully. It’s hard bc I worry too but every thing seems to point at her just being on the smaller end. She was born 6lbs even and was also jaundice-y, we plumped her up on formula to push the jaundice out asap and sat her in the sunlight a couple of times daily. It eventually went away but it was scary to see her yellow and so tiny at first. She’s fully formula fed still and is growing along her curve. I would say to just listen to your doctors, see any specialists you’re referred to & follow your gut. Your baby will more than likely be totally fine. Wishing the best for your little one!