First, don't blame yourself. You can be a total health nut and it wouldn't matter. This has nothing to do with you and your diet and everything to do with those hormones and the placenta.
My dietician recommended 30g or less of carbs with breakfast. 45g-60g of carbs for lunch and dinner. A snack between meals of 15g and a bedtime of 30g. But don't feel like you have to eat all the carbs allowed. My endocrinologist recommended 1/2 of this, so it really depends on the doctor. But the most important thing was don't look at the sugar content of food, but at the carb count. Nutella was something she told me to not go near, soooo much sugar. Instead peanut butter would be better. You want to balance your carbs with protein. Protein is broken down much more slowly so it stabilizes your levels and also makes you feel full longer.
Are you checking your levels during these weeks? If so, I found keeping a food journal with my levels really helped (and the dietician will want this anyways). I found that milk, even if it's my only carb, makes my sugar go absolutely crazy.
Don't beat yourself up. I know it's hard, I try my best every time I get a high # to remind myself that there's only so much I can do. I eat the best I can. Hopefully you have an amazing doctor who reassures you like mine does. Best of luck.