Week 29 3hr blood sugar increase

My blood sugar recently went haywire. My post meal 2hr blood sugar is within normal but when i tested 3rd hour it increased to 6.7 to 7. Especially when im about to sleep. I control my diet by consuming lesser carbs but why is this happening to me? Pls help im so scared my GDM is out of control. #gdm #pleasehelp #ftm #firstbaby #diabetes #bloodsugar