my son who is 8 and weighs 89 pounds has been constipated the last few weeks- we went to the doctor on monday and the xray clearly showed he was backed up. the doctor told him to drink 150 ml of mag citrate and put him on a stool softener named docusate sodium 100 mg. we have had 2 bowel movements since monday and they were very hard for him to pass- I thought that more would have come out by now ! does it take a few days for the docusate to kick in?