Low-Carb Diet/Blood Sugar?

Whenever I go on a low-carb diet, after about a day or two I start to shake. I eat right and everything like egg whites for breakfast with a granola bar and tuna salad for lunch. Why am I shaking? Last time this happened, I tested my blood sugar and my Mom said it was normal IF I WAS CLOSE TO DIABETIC which I'm not!!! Can somebody please explain why this keeps happening?