I've gained 8 lbs and I'm 25 weeks
Your body is going to gain what it needs to. Just try to eat healthfully and stay as active as you can without pushing yourself too far. And doctor will let you know if there should be concern about your weight.
I am 30 weeks and I have also gained 50+ lbs! As long as baby is healthy, you are fine. Every woman is effected by pregnancy different. This is #3 for me, and this is the least amount of weight I have gained.