Gestational diabetes

Has anyone who is already considered underweight get diagnosed with gestational diabetes? I am very concerned that I am going to lose weight by altering my diet so much. I just had lunch and my # was a little high 128 (supposed to be under 120). I feel as if no matter what I eat for dinner now my number is going to come back high. I may be able to eat a salad to fix it but I fear that by doing this often I am going to lose weight. I'm 25 weeks and have only gained a total of 7lbs.