barely gaining weight?

I'm 22 weeks pregnant and have gestational diabetes. The diabetes is diet controlled and my numbers are great, fasting in the low 80's and 1 hour after meals never exceeds 115. However, I gained approximately 3lbs only! My obgyn hasn't mentioned anything about it during our visits but I plan to bring it up to her at my next visit. I'm already overweight(263) pre pregnancy and I was set to gain between 11-20lbs for the pregnancy. Anyone else diet controlled with gestational diabetes and not gaining much weight? Any food ideas to increase calories but not carbs? I'm to eat 180 carbs a day and 2000 calories. Thank you.