Pregnant with blood sugar problems

Hi so I'm 18 weeks pregnant with my first. Before I got pregnant I was considered prediabetic. With diet changes and exercise I got back in the normal range. My doctors are still concerned about my levels throughout pregnancy. So I still test 3-4 times a day. Recently I've discovered that my sugar drops during the night while I'm sleeping. I'm not aware of this until I wake up and I feel extra groggy with a headache. Does anyone have suggestions to keep my sugar within normal range while I sleep? I eat a normal dinner, my sugar is fine before bed and fine when I wake up. It just drops overnight.