@khelves Welcome to Mayo Connect - when the poster said "You should be under a doctor's care for this" they meant that the inability to stay hydrated, in spite of drinking enough water, can mean there is an underlying physical cause for your low blood pressure. We are not doctors, but even a doctor would not try to give you a diagnosis without examining you. A physical with some lab tests can lead to the answer.

At 16, have you made your adults aware of the problem? Have you seen a provider for a full exam - I don't mean Urgent Care or the Emergency Room - they are just there to handle the immediate issue, and would just tell you to go see your doctor. If you do not have medical insurance, find a Teen Clinic in your area that can help you.