Good question. First, you may think you don't bleed a lot - maybe you bleed the same amount as your parent, or someone has told you that you're not really bleeding a lot. But, you might be bleeding more than you should in a healthy amount, and that might be part of the reason why you feel dizzy on your period!
Check out the section "How much bleeding is too much?" on this page - https://www.violetproject.org/menstrual-health
If you ever feel dizzy or nauseous or vomit while on your period, you should see a doctor. These more extreme symptoms could indicate an issue with your period.