I know hard to talk about. No pun intended. LOL. But... this has been a chronic issue for me for about 15-20 years. Started needing to take something daily beginning mid late 20's and now 44. I have tried everything. Kept trying perscriptions, but even if worked a bit, my body could not tolerate and I would stop due to other side effects (allergic reaction, chemical sensitivity,etc). So I began looking for natural, non-perscription supplements since in my case I ate plenty of fiber and drink lots of water so it was not a diet cause. Anyhow, a cleanse is a good place to start. A gentle one is "Whole Body Cleanse" by enzymatic therapy. A more powerful one is, "Ultimate Cleanse" by Nature's Secret. If that does not jumpstart your system back up...
I took the magnesium that Deb mentioned in both a pure magnesium powder and caplet form at different times. The powder is just magnesium without additives, which I like that, but it can cause you to run to the bathroom. Need to test to get right dose for you, but I thought I had mine down yet still had surprise emergencies. (start no more than 1/4 teaspoon in 8 oz. water or juice.) I found the Phillip's magnesium caplets worked without the emergency running. Recently recommended that to my aunt and she says it is working for her. There are also a variety of senna tablets and teas I have tried, but my body eventually adapted to the tablets and then I had to increase. Senna is a natural laxative, but still has addictive effects on your system. I do keep the tea in my house for when daily supps are not having effect and many days have passed and I'm uncomfortable. The senna tea I use comes in regular and extra strength. It's called, "Ballerina tea" and I've found it also under the name "California tea". Note if I take this I do it in the evening and do not leave my house the next day until I empty. It seems to take aprox 10-12 hours to go thru my system, but my family has used it and only 4-6 hours for some of them. Everyone I tell and who tries this for occassional needs says they are grateful I warned them it comes on strong and not to take unless they will be at home. So, I have tried a lot of different products and herbs over the years. Those are some of the standouts, but I have a chronic issues with hypomotility so I typically need more punch than most slow people.
Maybe start with something like FiberCon 1-3 times a day or the Phillips caplets mentioned as those are easy to get at your local store. If you don't mind the chemical, Miralax works really well (but gave me allergic skin reaction so I had to stop it). Also, pickup some peppermint tea as this is soothing to the gut and helps digestion. Ginger is good for the gut too, but not sure about helping constipation. Even though I prefer organic and this is not straight peppermint, I actually like Trader Joe's Mint Melange blend hot tea (they have straight peppermint too). I drink this in the evening sometimes after a heavy meal.
I could go on forever with all I have tried, but I will skip to the now. After having to keep switching between doses and senna vs magnesium and other things when body got used to each after a while, I researched specifically for a non-chemical, natural product that worked to stimulate colon peristalsis naturally, which is lacking with hypomotility disorder. Some constipation cases people just need a stool softener to retain water in the colon for easy passage and Colace (or generic thereof) does the trick; however, in my case I retain water fine, but require a stimulant of sorts for the colon muscle to work properly. Don't know if this is related to fibromyalgia or not, but I am big on finding each person's cause and treating the cause, not the symptom. The product I now take is a combo of all natural herbs and is gluten free, but I have to order online as I've never yet seen it in local health stores by me. I found my right dose and rarely have emergency.
For you, if the standard non-stimulant, Colace stool softener (or, magnesium - natural stool softener) doesn't work try some of the others, but unless have a specific known condition like mine I would never recommend someone take a daily laxative because your body will become dependant on it and then you have to increase over time to get the same affect. Your body will stop functioning on it's own naturally and you will end up on laxatives for life (which unfortunately will be my case), which is not good. I don't know your specific situation so I aimed to help you with over-the-counter, non-perscription product ideas from one extreme to the next in hopes you start with something mild, yet have alternate options to try if mild does not work for you.
This was an extensive reply, but if even one thing I said sticks with you (or someone else who needed feedback from your post too) and proves to be helpful then it was worth it. Please let me know. I'm interested in your progress.