Glucose Screening

I had my glucose screening last Wednesday and I got a call from the midwives yesterday telling me that my screening came back abnormal. I'm going to have to take the three hour test on the Wednesday coming up. I'm a little worried about this because I've been determined to have a natural birth. I don't know how possible that will be if I have gestational diabetes. I have been feeling really strange lately, even a few days before my glucose screening. It's as if the energy that is supposed to be coming from my food never leaves my stomach. My stomach can only hold so much, so I basically have to go around feeling weak. I wonder if this is a normal side effect of just being in the third trimester.