I applaud you for what you want to achieve. You know someone of your age could start going down the wrong path(s), but you have chosen a path of physical endeavour and improvement, which is better for the rest of your life and you should be so proud of your choices but also for your frank, honest and in some ways beautiful admissions about yourself. I fully appreciate it can be hard for someone to admit publicly, they have a condition, when it's not something apparent, or it may be something they find difficult to discuss, so you have my fullest respect for everything you have said here
I know it will to some extent be made harder by the Hypothyroidism and the potential side effects of using medication to treat the condition.
You are not the first person on here who has attempted to acheive better physical wellbeing with a Thyroid condition, so I can tell you from my observations, it can potentially be quite a bit trickier than just trying to achieve ballpark calorie totals per day and sticking to sensible choices of food where possible and certain types of exercise.
As long as you keep believing though and are not hard on yourself whne you do "human" things and occasionally slip up, you'll be fine and I really wish you so much luck, because I think life has given you a bit of a bum deal in some respects and I think you're the sort of person who deserves some luck and a lot of happiness, so if there is anything at all we can do for you, please just ask and don't apologise for it okay
GOOD LUCK to you and very, very best wishes.