8 kg.... i wish!!!
I think that i had put on about 20kg maybe a bit more for my pg.
My OB told me to not worry about the scales and refused to weigh me (let me do it myself - but it came with a lecture each time)

I think by the time i hit my third trimester the weight continued to go on, but it slowed a bit, maybe as i felt full a lot more i dont think a kg a week, i think that is more in the last 4 weeks not the whole trimester.

As long as you are healthy, you are eating the right stuff (be it a little too much at times ) i wouldnt worry.
How is your BP?
Are you drinking enough fluid, sometimes thirst can be mistaken for hunger, i was drinking tonns of water when i was pg.

to BB BTW
If you havent already, maybe check out the belly buddies section and find the group that you fall into so that you can chat with the girls that are due the same time as you, this helped me heaps and i found that most of them were going through the same thing or had similar questions to me

HTH