My son was born 7 pounds, 14 ounces and weighed 7 pounds, 6 ounces at a month. That scared me being a ftm but they say babies loose weight before they gain. Hes now 2 years old and is.2'11 and weighs 36 pounds. I dont think you have much to worry about unless it continues
Its normal to loose a lil bit of weigh at first they are still getting ajusted to feeding them selfs .. And at that stage they can be very lazy at eating .. It should pick up very soon !!