Can my son take melatonin at night he's on vyvanese and Trileptal he's not sleeping at night?

Yes, it's possible. Melatonin may help with sleep but may impact growth. Be sure you have done all the appropriate sleep hygiene steps- no caffeine or chocolate, same bedtime, no electronics, give vyvanse (lisdexamfetamine) at same time every day. Adhd patients often have difficulty with sleep. We use Clonidine to help order sleep architecture and improve adhd symptoms at the same time. Be sure to talk with doctor about these problems.
Yes, . But he also needs to have his meds doses looked at as well as a possible sleep study or work up for other causes of not sleeping.
Yes. Melatonin is safe for most patients and does not have significant interaction with other meds. Advantages of melatonin: works quickly (1/2-1 hr), no hangover next day, non-habit forming disadvantages: doesn't last through the night (if patients have lots of awakening through the night, may need to consider other potential causes of sleep disturbance), may stop working over time.