Maybe your baby is just growing fast and healthy. Not much to worry about. I knew a lady who was huge! Like her stomach was going to fall off and her baby only weighed almost 8 pounds! You could be holding a 10 pounder in there! Or your calculations could be wrong. The peiod before the one you mentioned might have been spotting and you were already pregnant so your a few weeks ahead now. If everything fine, then dont stress over it. Good luck!

....This is what other pregnant women used to call me in my prenatal class!I dont know if ots the same,or if its any consolation,but at 3 months , I looked as if I was 6.By the 5th month I looked as if I had twins...By the end of the pregnancy,i "popped" my knee,under the weight....
It was mostly amniotic fluid(while in labor,my baby kept "swiming"in me,we could see her move.It was surreal).
She was big though, nearly 4 kgs.
I wouldnt worry too much....
People come in all shape and sizes,...And so do babies....
Thats my opinion.
Relax and enjoy it,cause this is a magical time.Literally!

Hello I always measured big after about the 18 week too. The doc said I was just going to have a huge baby.Wich scared me a little. But my children were only 6lbs11oz and 8lbs2oz. So don't worry and just enjoy your belly.
Rae-anne