Weight gain

I know every woman is different, but this is my case. I am a plus size woman, and my doctors told me that I should try to only gain 15 pounds during pregnancy. In the first 20 weeks, I was doing very well, and only gained 5 pounds. I just had another visit yesterday, and in the last month, I gained 3 pounds! I kind of expected that, because in the last few weeks, I've been hungry ALL THE TIME. I know it's only 8 pounds so far, but with the rapid weight gain in these last few weeks, I'm worried that I'm going to gain more than the 15 pounds that I'm suppose too! The doctor told me that my weight gain couldn't be more perfect...but I can't help to worry. I try to eat as healthy as possible, and keep active. Any other advice?