I think if you re-read your first message and imagine that you are giving advice to yourself, you might find that you've answered some of your own questions. For example, this is what I see.
1. You posted your message to the Healthy Living group.
You recognize that you need and WANT to improve your health. You're already on your way.
2. You've already had success with managing your behavior. You have the will and the determination to apply strategies to help yourself.
3. Do you have to choose between college planning or your health? I think you can do both. Take small steps, but make them move toward your goal of living healthier. That includes healthy food choices, physical activity and doing things you enjoy. Perhaps planning for college will give you that joy and purpose.
Do you see a therapist? Have you heard of cognitive behavior therapy?