That's too bad - chronic dehydration and thirst symptoms are worrying. Is it that you are truly dehydrated because of an oversight in liquid intake or is there an actual medical condition that we are just putting a band-aid on? More comprehensive tests and a consult with a medical professional is required. Sorry to hear that you'll have to wait - go ahead and make an appointment. Voice your concerns and have a formal evaluation. This needs to be medically evaluated if you are chronically dehydrated at this age to the point where you experience symptoms. This worries me.
Like other suggestions, increase fluid intake by incorporating juices and flavored mixes. Add fruits and veg high in water content. Apples, berries (strawberry, blueberry), banana, melons (watermelon, cantaloupe, honeydew), citrus fruits (orange, grapefruit), spinach, lettuce, celery, carrots, green peas, zucchini, cucumber, broccoli, cauliflower.