normal skinny; no pills; about 10-11 kg or less available to loose

Your BMI is 18.4 This is normal. North American skinny is normal in many other countries. You will gain weight when you gain muscles. You may have slightly disturbed your digestion, but the information you give is too scarce for anyone to get a good understanding.
Intermittent fasting may be the answer for you, as of now. If you want to fast longer I'd recommend no further than BMI 15 or to about 47-46 kg, which gives you about 11 kg or 22 pounds to go down, provided you have about 25% fat; if not - less pounds to loose. It would be extremely important at that point to re-feed gradually and to restore your mass at least up to 58 kg.
If you continue taking ADD medication it may make the task of gaining back very hard. Also you should not fast if you are on pills. Stop the pills first with or without help. I know these may give you Depression or other disturbances if you stop cold turkey.
Best,
DL