Definitely not menopause. Changes in perceived body temperature are often a symptom of a dysregulated nervous system. Fasting can be stressful on your body in different ways than you’re used to. So your nervous system may be like, “wtf is going on right now?” You also mentioned ADHD meds, which 100% impact nervous system regulation. I’m guessing that the combination of the two is sending your body into a state of hyperarousal (hot flashes can be a symptom). Feeling cold can often be a symptom of your nervous system being in a state of hypoarousal. Your dose of ADHD may be too high while you’re fasting.
That being said, I’m not sure if you have a history of trauma (ADHD meds are often prescribed to cover up symptoms of trauma), but it could be bubbling to the surface. I would recommend speaking to a doctor or licensed therapist who specializes in trauma (look for someone who is trained in somatic experiencing, NARM, or EMDR).
I have an unrelated/related comment. When I did whole30 elimination diet, I could no longer drink coffee. Even the weakest possible brew in the morning would give me a sleepless night and a headache. So, I guess some food that was making me drowsy, was helping to digest coffee, wasn’t there and coffee was too much. That being said your medications can metabolize differently without food, dosage may need adjustment, the digestive system may not be happy to interact directly with certain meds. There’re a lot of possibilities of the causes, but it’s not a normal typical body reaction to fasting and I’d chat it out with a doctor.