My son Jai was 4640 grams or 10lb 3 oz at birth and he too, was completely breastfed and weighed 10.6kg or 23lb 8 oz at 16 weeeks, he was then started on solids .He was a chubba. By 30 weeks,his weight gain had slowed a little and he weighed 12.3kg and he was 13kg at 40 weeks-still a big boy.He started walking at 12 months and started to thin-out pretty quickly due to his activeness.Jai is now 7 and is no bigger than the average boy his age.He just had a good start .
My second Son Eli was 4840grams at birth or 10lb 11 oz and he too was fully breastfed -he was 9kg at 16 weeks and 10kg at 22 weeks but never looked like being the bouncing bubba that his brother was even though I had done everything the same for both of them.
I think if there was a family history of obesity,you would have to be very careful and monitor your baby's diet and calorie intake but otherwise I'm sure he too will lose the baby-fat once he becomes active.If you are really concerned,ask your Dr,but
In the meantime,just give your big,cuddly bubby plenty of hugs and stop stressing.
Julie~mum to Jordyn-12,Jai-9,Eli-5,Kayne-10months!