Hey Tish
I agree with DieSwartKat.
With my first pregnancy I picked up 30Kgs, because I believed I had to eat for two, I never lost it, and my gynae (Female) never said a word about it.
With my second pregnancy I picked up 7kgs, I tried to control what I eat, I also suffered with heartburn a lot.
With this one I am constantly hungry, I have picked up 400g so far.
What Im trying to say is, just as long as you eat healthy and rather smaller meals more frequently than bigger meals at set times everything should be ok. Also make sure you excersice a bit everyday even if its only going for a walk around the block or go to the malll have a nice window shopping trip.

I know people severely obese and went through pregnancies delivering perfectly healthy babies without any probs.
btw. I am now 10 kgs heavier than I was the day I gave birth to my now 5 year old son. And I have a plan worked out to shed this after this pg
Good luck and dont let others ruin this special time in your life! (((hug)))