I also had gestational diabetes when pregnant, and thought I'd offer my own experience. I have found that when I feel the way you described, it is almost always related to dehydration rather than nutrition. Light-headedness is one sure sign (something I used to think was related to eating) and weakness is another. I've been riding about 100 miles a week through the winter and need to meticulously watch my water intake. I have to force myself, usually, to drink much more than I want to... and find that when I do, my energy, focus and general sense of well-being picks up in an hour or two. I'm so used to paying attention to eating (as a woman), and constantly underrate hydration.

for what it's worth.