Dizziness can be a symptom of many things- from simple dehydration, food allergies, or a health problem as you mentioned.
Frequently "vertigo"- or dizzy, unbalanced sensations are caused by inner ear issues- infection or fluid in the inner ear. Have you recently had a cold?
Diabetes usually includes extreme thirst, frequent urination, and some other symptoms as well. Do you have those symptoms?
"Journaling" may help you and your doctor solve this mystery.
For two weeks or more, try writing down absolutely everything you eat or drink- and all of your activities, even your feelings and important events. Include how much sleep you got and the quality. Write down the time of day when you felt dizzy or light headed. Soon, a pattern may become clear.
There could be a connection with something that might not seem like a big deal- caffeine/energy drinks, eyesight/computer or cell phone screen time, specific trigger foods, etc.
When you are ready to see your doctor again, take your journal to the office and you can show him/her some of these patterns.