Does this mean I'm not ready to eat this kind of stuff yet?

I tried ONE wheat free, yeast free, dairy free waffle with some almond butter this morning. A little later, I felt so tired. Is this a sign that I may not be ready to eat things like this? Up to this point I've only eaten baken chicken, tuna, eggs, and veggies. Since my diet has been pretty limited, I'm not sure what to expect when I eat something I may not be ready for. What are the signs? How do you know?