I am 36 weeks tomorrow and I've gained 12-13kg already. I'd expect to gain about 15kg all up. I gained about 13-15kg with DD. I lost it pretty easily so I'm not too stressed.

But I weighed a lot more pre preg than you so I don't have the capacity to gain as much as you have. The thinner you are, generally the more weight you will gain. For your height it sounds like you were very thin pre preg.

I don't follow the 'rule' that you put on most of your weight in the third tri either. Both times I've put the majority of my weight on in the second tri and hardly any in the 3rd (which did stress me out in the second tri wondering how big I'd end up if it continued!! Thankfully both times it slowed right down by about 30 weeks).