.1. I take my multivitamin, 5-HTP, L-Tyrosine, Choline, Loratadine, Singulair, Valsartin and ADHD meds in the middle of my fast when I first wake up.
.2. The precursor amino acid to melatonin (and serotonin) is 5-HTP. I’ve had better results taking this in the morning than taking melatonin at night. As always, ymmv…
.3. Depends on how “clean” you want your fast to be. Metabolically, the sweeteners in the gum are going to cause an insulin response which will reset the timer regarding the benefits of being without insulin for extended periods (like lowering insulin resistance) but you’ll still be benefitting from a calorie deficit for pure weight loss. It also might make you more hungry when the gum causes an insulin response, stops energy production from fat burning but there are also no actual calories coming in.
It’s like exercise, if you cannot do the form perfectly there is still gains to be had doing it the best you can until you can do it perfectly.
In answer to your 2nd question, most dissolvable melatonin will break a clean fast. I get mine in these sleep electrolytes which also have magnesium glycinate which is amazing for sleep. https://www.amazon.com/Reset-Electrolyte-Electrolytes-Melatonin-L-Theanine/dp/B094RFF6RC/ref=sr_1_5?crid=1OGMCZKB3VF7T&keywords=reset+electrolytes&qid=1677517185&sprefix=Reset%2Caps%2C135&sr=8-5