rapid weight gain?

At 38w1d I had gained 6 lb in the last 10 days. Increasing discomfort. No change in eating. Have even increased activity. I've had typical weight gain throughout pregnancy until now. I'm a bit worried about it being fluid, polyhydramnios. The doc did not seem at all concerned or surprised by the sudden weight gain. Has anyone had similar experience? Any risk with polyhydramnios? I don't know what's happening and it's concerning me. I'm so uncomfortable, I want this baby out so bad.