When I don't eat enough food I get lightheaded, dizzy, and feel like I am about to pass out. What could it be? Could it be low blood sugar?

Low blood sugar. the only way you can really tell if it is low blood sugar is to do a glucose check when you are feeling shaky or lightheaded. I would suggest just making sure you eat a snack or a protein bar when you are feeling this way. Always eat a good breakfast in the morning. It starts off your day in the right way. Good luck and feel better!
Hypoglycemia. It could be hypoglycemia. Serious hypoglycemia (low blood glucose) is unlikely in those who do not have disorders of insulin production like diabetes or reactive hypoglycemia. Symptoms like you describe may represent a natural response of the body to prevent hypoglycemia -- particularly if they improve with eating. A glucometer could answer the question for sure. Any glucose below 70 is low.