That is easy.

Simply take Vitamin C and increase dosage until you get loose stools.
https://www.amazon.com/Foods-Vitamin-Crystals-Ascorbic-Pound/dp/B0013OUMVO/ref=sr_1_8_s_it?s=hpc&ie=UTF8&qid=1474839339&sr=1-8&keywords=ascorbic%2Bacid&th=1

I suggest starting with 1/2 tsp and slowly increase dosage until you get loose stools.

Grizz

I eat four or five prunes a day.

maybe try some potato starch - it feeds the bacteria in the lower intestines.

also as mentioned you could take Vit C to tolerance or some forms of magnesium like oxide iirc will also pull moisture into the intestines but i dont think these solve the underlying problem.

also, i have heard that aloe vera juice is very good for the inner surface of your intestines, as is the amino acid l-glutamate.

Calcium carbonate will cause or increase the tendency to constipation! It's very poorly absorbed by the body unless it is oxidized by stomach acid, in which you might be deficient.

Magnesium sulphate (Epson Salts) can loosen the bowel as can Magnesium citrate.

Lecithin can also be helpful and has many beneficial effects. Combining them and eliminating calcium carbonate should get things moving.

You might try reacting the calcium carbonate with an acid in how water and maybe a hand blender and see if you can get it to react. I have some calcium carbonate and found it very difficult to get to react with acids. It should turn clear when fully reacted but I have never managed to get it to do so. Releasing the carbonate, which is alkaline from calcium carbonate is very difficult unfortunately.

Malic acid can be used, ascorbic acid is not so useful due to needing hot water and the damage it can do to vitamin c. It might require a stronger acid such as HCl but if you are deficient in that then you are out of luck. It would be better to get a more absorbable form if you really need calcium. Using bone broth soup would be a better source IMO.

I agree with high-dose Vitamin C, 2,000 to 4,000 mg per day upon waking and well before the first meal. Take with some water. 1,000 to 2,000 mg can also be taken before bedtime, but probably not over about 4,000 mg per day altogether. Fiber actually turns out to be harmful in the long run according to http://gutsense.org

I've just started Vitamin C myself. The first day I had two small BMs and yesterday one big BM. Today I haven't had a BM yet, but transitioning to a low fiber diet is said to sometimes involve less frequent BMs, due to less fiber. After transitioning, it's said that BMs tend to occur after each meal and are almost unnoticeable.

Vitamin C is said to be the only laxative that has zero side effects.

I'm also on low carbs in order to kill off Candida yeast infection. I'm using coconut oil, garlic and olive leaf extract to kill it. I need to get L-Glutamine which is said to be needed for the mucosal lining. Fiber is said to be hard on the mucosa and the microflora.

I think the site I linked above is the most important health finding of the century at least for North America.