This is a good question for your Dr. ONLY they can decide personally how much you should be gaining. Some women need to gain more than others, some are ok to gain less. I'm 37 weeks and have gained 15lbs and when I was 7 months I had only gained 5-7lbs and my Dr. was ok with that, but it's different for everyone, and your Dr. needs to tell you what's best!
The other thing is that you might have gained more than that in baby-related poundage and lost a corresponding amount in you-related pounds, if you had any extra to begin with. A healthy diet can do that -- you stop eating the junk because you are pregnant, and lose weight on your excess areas while putting on the necessary weight for the baby in the baby-related areas.
I call it the great pregnancy shift,lol. With y first two I didn't gain an ounce until my last trimester and then WHOOSH it came on fast. Granted a lot was water weight and such, but it was still wild!
With this one I am following their desired progression of weight gain.
Andi