As noted already, food requirements are fairly individual and the best person to consult is yourself. If forced to guess, I'd say, for your size and weight, planning on a 3000 calorie/day diet ought to be sufficient, depending on your daily miles. I wouldn't go below 2800/day because it sounds like your metabolism is a barn-burner. But even better would be for you to track your current daily calorie intake on days when you are pretty active, then use that as a starting point for deciding what you'll need on the trail. Walking uphill under a load requires fuel. The Nutrition Information labels on food packages are your bff.
To get any kind of reasonable total pack weight you will need to resupply yourself with food along the way, ideally every five days or so. Look for food that averages out around 100 calories per ounce (or about 4 calories per gram). Any food with a low water content is likely to be in this neighborhood, but remember to drink lots more water to help compensate for the low water content of your diet.
As a general rule, the lighter your pack weighs, the happier you will be. Anything approaching 40 lbs. will feel like a ton to you. If you can't hit a target pack weight of 30 lbs or less, including food and water, then at least get as near to 30 as possible. This site contains a wealth of information for keeping your pack weight low without spending a small fortune or endangering yourself by leaving out necessities.
Some basic rules: The lightest things in your pack are the items you don't bring. You only need enough clothes to stay warm and dry when you're wearing everything you have with you, plus one change of socks. Leave the cotton at home and bring quick-drying synthetics. If you have a limited budget, I'd advise you to prioritize the sleeping bag as the one piece of gear not to scrimp on. The most important thing about your pack and your shoes is that they fit you correctly. Practice with any new or unfamiliar gear at home before you go. That means set up your tent or tarp, light your stove in the wind, wear your shoes or boots, test anything that's supposed to be waterproof to make sure it is.
If your parents are OK with your doing this solo at age 14, you probably have some camping/hiking/backpacking experience already. I didn't solo any distance until I was 18. The best piece of advice I can give you is don't be afraid to bail out if things go wrong. There is no dishonor in knowing when to stop. Persisting in an error is the best way to get into deep trouble. Next best advice: have fun!