Could just be your body holding water as long as your eating healthy and exercising youll be fine I've gained about 6-7 lbs but I'm 32 weeks
I gained weight fast as well, it slowed down, a lot, in my third trimester.... My doctor just knew I was going to have gestational diabetes because I went over the expected weight gain, but I don't....
I'd let your dr know. Probably fluid retention.
You should definitely tell your doctor..
I just now hit 9 pounds and I'm 29 weeks.
Although you may gain most of it in your first to second trimester.
Just drink a lot of water!