Whole day feels pressure to pass motion.

I m in 3rd year of my graduation. When i was in class 10, i had braces treatment but even after 2.5 yrs of bearing continous pain & discomfort due to braces, my treatment was unsuccessful & rather it worsened & i developed inefficiency in chewing. After that  setback, i developed the problem of constipation. Done various times treatment from doctors for constipation but no relief. Took varoius laxatives & med for 1 year under guidance of doctors but no relief. In blood tests it was diagnosed that my Vit D3 level & Hb is very low. Took medication for that also. Presently i drink 8-10 ltrs water/day. 3 ltr warm water in the morning itself in 1-2 hrs to pass motion despite taking movicol sachet and sit in the toilet for 3 hrs & still not satisfied with my motion. Again after 15-20 minutes i drink 1 ltr water but more stool doesn't pass. Whole day i drink water and go to toilet, and this cycle continues. Not feeling hungry, gastric pain in chest, stomach and back. Feel tired.