Rapid weight gain

At my 20 week appointment I had only gained 9 pounds, which my midwife was happy about. Now I am 23 weeks and since then I have gained another 7 pounds! I haven't changed what I'm eating, although I have been eating slightly more because I get hungry more often. 7 pounds in 3 weeks seems crazy to me, especially since I started out overweight. Anyone else gain a lot all of a sudden in the second trimester?