fasting is excellent, but diet is crucial

Arcus said it right about the food you eat in general and also after fast.
If you are suffering, regular fasting like 5 days a month could be your fastest way to health and no pain. Kids and teens are also very toxic ans inflammed in our reality and I have seen this age group do extremely well with short fasts, given though a PRISTINE diet is then adopted.
No fried food.
No processed food.
Minimal to none animal source food.
BUT you need to start having lots of organinc fruit, load on berries and melons, watermelons, green juices (you may want to follow liferegenerator on youtube), culturize raw nuts (as per him or Lou Corona) and in general, as Arcus pointed out: going vegetarian, hopefully Vegan, while best would be: raw vegan.
Good luck, kid, and let us know how you are doing!
DL