36 weeks, feels like I can't eat or drink enough to support us both?

I will be 36 weeks pregnant on Monday. 8 years ago I had gastric byp surgery to lose weight. This hasn't really affected me that much during my pregnancy other than some vitamin deficienciess. Thing is the past few days it feel like I cannot keep up with the needs of us both. I am so hungry and I eat, then like 2 hours later I'm hungry again. I eat when I need to and eat good foods to try to keep fuller longer but its not working. I had gained only 5lbs so far and I have lost that in the last week. I am so thirsty no matter how much water i drink I am still going to the bathroom all the time but its never a full bladder. Does this mean I might deliver soon?