It's normal. On my first son I gained like 30 pounds.. on this baby I lost weight at the beginning and every since I've been the same weight. My doctor says it's actually good as long as you are eating and the baby is still growing. . Only time to worry is if your not eating anything. My doctor gets super happy when he sees my weight and I tell him that I eat alot.
I've gained 2 pounds my whole pregnancy I'm 37 weeks right now and the only reason I know is cuz my ob walked in the room and told me with an that is so awesome attitude so I'm guessing it's normal.. Lol my son is measuring right on track... So I wouldn't worry too much about it...