Aww, I get your worry, mama, 2.7kg at 37 weeks is on the lighter side talaga, pero 500g gain in a month is actually decent progress! Since he's feeding well and the doc cleared him after immunization, sounds like he's on track, just a naturally petite baby (like some ng aming mga kaibigan's LOs na ganyan din ang features). Basta he's alert, pooping regularly, and gaining, he should fill out more in the coming months, every baby has their own timeline, pero if you feel something's really off or he stops gaining, better check with his pedia para sa peace of mind, 'cause mama anxiety is real and deserves answers!