I feel nauseous, and light headed when hungry. Why?

I am trying to lose weight, it is very hard for me. I am not Diabetic. I have been tested many times. Recently I was tested to. My doctor told me to have snacks. With work I do not always have the option since I am a training Veterinarian assistant. I have to deal with patients. I am always on the move. What is wrong with me. I eat regular meals. I am just eating healthier.
I feel nauseous, and light headed when hungry. Why?
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