When I was far better than now I'd take some Probiotics and milk kefir which helped me a bit. Togheter with diet I was able to have a bowel movement each other day.
No milky no sugars no bread no beer sweets ...I did not know then about candida diet I was just observing what food was constipating me. There are also bacteria or protozoa which can feed on these not to mention worms.
But since the culprit was not clearly identified and I was giving up diet - the problems came back. A misdiagnostic put me on Antibiotics and that was it. For me then was giardia candida and a bacteria overgrowth in the colon. Later were more...
Sd is very right - IBS is a major bs. I was on this so called diagnostic for years. I've discovered since now like 5-6 infections in the gut making private tests on my money. No wonder I have IBS. Still my GP prefers the stress influence approach. :) lucky me.
Try control it with the diet first see what helps. As soon as you find the culprits you can better target treatment.
Movicol and lactulose are not proper for this condition.