Brief Answer:
Quite a few causes could cause this ma'am

Detailed Answer:
Hello ma'am and welcome.

Thank you for writing to us.

I have gone through your query with diligence and would like you to know that I am here to help. Well ma'am, your symptoms can appear due to a host of conditions, but I would like to list some of the most common ones:

+Low blood sugar: More often seen in young women your age, especially due to long gaps between meals, diets, etc.
+Related to the menstrual cycle: A hormonal change can also cause slight lightheadedness and a headache, which is self-limiting and usually resolves with time as the hormone levels return to normal levels
+Thyroid abnormalities
+Conditions that can cause hormonal imbalances (e.g. polycystic ovaries)
+Rigorous exercise
+Temperature fluctuations
+Stress
+Anxiety
+Chronic conditions (e.g. diabetes, hypertension, etc.): Usually also present in family history
and a few other conditions

If at all you can relate to any one of these conditions, then do write back to me for further guidance. I do feel the first cause is likely taking into consideration your age, and if it has been a while since you ate or if you hardly ate anything, then this is easily the cause for your symptoms.

I hope you find my response both helpful and informative. Please feel free to write back to me for any further clarifications, I am always here to help.

Best wishes.

---