FWIW, medication can be a lifesaver. It's not always the answer, but for some kids it can really turn things around. A child who is always on the edge of a meltdown isn't able to learn coping skills or alternative ways of acting, and sometimes using medication to help them control themselves brings the kiddo to a point where they can work on those strategies.
desperate, I'm curious about the dose of melatonin your son is on. We also use melatonin with our ds to help him feel sleepy, but after some experimentation and reading around online, we found that it took a surprisingly small dose to get the benefit. Larger doses can make things worse for some kids during the day following, but it's not always easy to make the connection. My DS takes 1/2 mg every night. If we give him more he tends to be more disruptive the following day and to also have kind of a crash after lunch. He was even falling asleep at his desk at school! Other parents have reported nightmares or more aggressive behavior during the day after using melatonin. The standard tablets in drugstores are often 3 or 5 mg, and even the medical literature talks about giving kids as much as 10 mg, but anecdotally it seems like that may be far more than is needed. Just something to think about! We buy 1-mg dissolvable tablets from our HFS and they snap in half easily, so that he only get 1/2 mg per night.