My stomach has been measuring a few weeks ahead since 30 weeks. At 31 weeks they did an ultrasound and said he was already 5lbs and at 35 weeks and a few days they said he was 7lbs well see how big he is when I have him Monday lol my first was 8lbs 13oz 22 inches long
It could be something as simple as the position your baby is in. When I was 32 weeks I measured at 38 weeks just because my son was facing my back and was breech.