I have been suffering from constipation for 3 weeks, neither movicol nor dulcolax worked and after an x-ray was done and showed faecal loading, my doctor prescribed kleanprep, which worked on the day, but a week later, i'm constipated again.

No other disease?: Each person with constipation needs to be sure there is no other disease causing it. If constipation is just due to slow movement of the food and poop through the gut, then the things to try are vegetables, water, prune juice, prunes, fiber plus water, Miralax (polyethylene glycol) Senokot or other senna, milk of magnesia, etc... A doctor can evaluate, and might prescribe Amitiza or Linzess.