Dehydration can certainly affect how you feel and make you tired, sluggish, etc. It can also make your eyes feel dry and red. Make a habit of drinking water throughout the day. Carry around a water bottle. If you don't care for the taste of water, you can always add a little lemon juice or buy flavored waters. But make sure you are drinking plenty of water! You should be getting at least 8 full 8 oz's of water a day.
Also make sure you are eating at least every 3 to 4 hours. Breakfast is especially important because your body has already been fasting all night when you've been sleeping. If you're not normally hungry in the mornings then just make a fruit smootie or something in the blender. It's nutritious and will give you energy. Throw some fruit like a banana, frozen strawberries, blueberries, etc. in a blender with a little milk, sweetener and you can add protein powder or wheat germ to make it even healthier. Try and have a light snack in the afternoon like an apple or granola mix. You don't have to eat big meals, just try and eat healthy meals and snacks every 3 to 4 hours.
If you start doing these suggestions, I think you will start to feel better and have more energy in no time. If you stll don't after a few weeks of trying these suggestions, then get a physical done and get your thyroid checked. You're young, though, I think it's just your diet, or lack of, that's affecting how you feel. Hope this helps!
maybe your not getting enough protene or vitamins in you.