When you talk about liver detoxification, I think low methylation. When you talk about constipation and weight gain, I think low thyroid, which also impacts detoxification. I know that Iodine can fix whatever is a low-iodine problem and that there are relationships among all these factors.
Maybe you would be helped by a liver flush. It has been mentioned by many posters here and on CureZone in general. You can search for more on that.