GD screening is standard procedure at 28 weeks whether your pregnancy appears totally healthy or not. Did you not do the glucose tolerance test with your first pregnancy? If not, they make you drink a glucose filled drink and test your blood an hour later. It has about a 15% false positive rate. If you test positive they'll make you take the 3 hour test, which is more accurate. However you can usually request alternatives to the traditional GTT like the jelly bean test, juice test, or high-sugar meal test. Just ask and if necessary bring in suggestions for alternative tests if you want to go that route. Often you can also decline the test all together, but then they would need to treat you as if you did have GD for the rest of your pregnancy (not good).
As for weight gain, I am one of those that is always hounded to gain more weight as well. Some of us simply grow babies with less weight on our frames. It doesn't mean we are necessarily unhealthy or that our babies will be small. I was underweight starting out with all three of my pregnancies. I only gained 26 with my first and 22 with my second. Both times my mw's freaked out on me. I did everything I could to gain more... I kept track of my calories and protein intake for weeks. I tried stuffing down extra snacks between meals. I basically cut out exercise from my routine (except a bit of walking). I substituted full fat yogurt for the nonfat I prefer and tried to eat a ton of avocados. I didn't matter. I gained what my body wanted to gain. Both my mw's wanted me to go in for growth sonos (which are highly inaccurate in the third tri anyway). As it turned out, my first was 7lb1oz and my second was 8lb2oz.
Good luck!
