Babies weight at 31 weeks!

So my doc just did an ultrasound today and said my little man was weighing 3lb14oz said he is really big. Measuring 2 weeks ahead which is why they think I have gestational diabetes. But I haven't gained weight and don't have any extra amniotic fluid. Could I just be having another big baby?? My last pregnancy my daughter weighed 8lb 14oz at birth. What is everyone else baby weighing?