Have you done any of the things that have been suggested since you started posting here? If you do a search, you will find answers for most of your problems. I can't imagine a colonic will directly result in weight gain. It will cleanse the bowels and possibly allow your body to get the nutrients it needs. That said, it is probably best to cleanse then rebuild. A proper diet and workout program will help you gain weight (provided you want some muscle). There are natural ways to chelate metals. Do some research.
This way of life is a lifestyle change. Not a quick fix. You didn't get that way overnight. It takes time. Even when you find a solution, you may need to tweak it weeks or months from now because your body is no longer the same (i.e., hopefully better, not worst).