I have had problems with constipation as well, due to large polyp that will have to be removed. It is important to check this out with your doctor to see what the problem is. A colonoscopy is not that bad. I put it on the same level as going to the dentist, but not as bad as having a filling. (I hate that drilling sound)
Colace is a stool softener, but has little or no stimulative effect. The ususal dose is 200mg. daily, but sometimes it requires a higher dose. It can take a day or two to work, and you should use it for a few days. Lactulose is another stool softener that works better for some people who don't have success with Colace.
Laxatives with a stimulative effect can cause problems and dependence if used too often.
Fiber such as metamusil and benefiber can help draw water into the stool to soften it and build bulk to the stool. It is really important to drink lots of water, and more water with fiber (and all constipation problems). If you take a lot of fiber with not enough water you can make "concrete" and then it is really stuck. Add bran cereals, fruit and prunes or prune juice to add to your fiber. You really need a lot more fiber than most people get. 25 grams of fiber daily is reccommended and that is a lot more fiber than you might realize. I have found two tablespoons of ground Flaxseed is also a good fiber to add to you bran cereal.