Well, I think your body is going to do whatever it is going to do, BUT, that being said I noticed that I was gaining weight much faster than I did with DS1 (I only gained 20 with him, and I have already gained 16 with this one). It bothered me, even though according to conventional thought I didn't gain "enough" last time. I also knew, though, that I wasn't as active as I was last time. This time I am a stay-at-home-mom and I hardly exercise (bad!) and last time I was much more active and was also working on my feet throughout my pregnancy.
So, I started eating smaller, more frequent meals (since I noticed that even if I ate a big meal, I'd be hungry a couple of hours later anyway... so now I eat half my meal and then half a couple hours later). I also started exercising more- walking with hubby, biking, hiking, etc. My weight gain has slowed but is still on track. You certainly don't want to start losing weight (though you may lose a couple of lbs right before labor).
Your body might still gain as it is. It's okay- it knows what the baby needs, and it also knows what your needs will be after baby comes. That extra weight is CLUTCH for breastfeeding. I snapped back to my pre-pregnancy weight and size within 2 weeks of giving birth. That seemed great, and I was still eating A TON of food (I was much hungrier than while pregnant) but I was also VERY fatigued and would have frequent low-blood-sugar spells. A few extra pounds for a few months post-partum are necessary. Breastfeeding does far too effective a job of taking it off, sometimes :)