Hi Serena,
I would have to agree that there is no 'normal' as far as weight gain goes... Some people can put on very little, and may even lose weight in their first trimester.
And some people can put on a lot more, like me - who put on 40kg 8-[

I started noticing my weight gain very early in my pregnancy - I even noticed that I was putting on weight before I had even found out I was pg!