D.M.
Oh goodness, I have been there and done that. But, here's the thing my son's Pedi told me about laxatives and suppositories they cause more harm than good. Bowel Movements are a result of your body getting rid of waste that was not absorbed and the function of bowels can be disrupted by use of such products. When using these products too frequently your body doesn't have to process the movement and then can lose the ability to do so, and cause major issues.
What I do with my son when he's constipated is give him a daily cup of diluted prune juice or those wrapped prunes that are sweet and nicely packaged. Also, I put the daily amount of water he 'should' be drinking in a jug and try my best to get him to drink it. We keep a snack tray of high fiber veggies and fruits and also crackers.
According to our Pedi, a bowel movement daily is not necessary at this age and what's regular for one child is not regular for another child. More than four day without a movement (soft mushy) is considered constipated by most standards. Also, kids even at this age can experience potty anxiety if they are being made to poop or if they are having painful or uncomfortable pooping experiences. Just keep it simple and don't stress about it. Keep a diet that is high in fiber and lots of fluids so that stools are soft, and maybe get a 2nd opinion before continuing the over the counter products.
This link is very helpful:
http://www.babycenter.com/0_constipation_11419.bc