Problem in rectum. Of doing surgery?

I had subtotal colectomy(ascending to sigmoid anastomosis)(colon inertia)on 27th march.Doc did not perform total colectomy because he feared loose motion.I was fine after surgery(stool coming out in full force and felt satisfied)then this feeling started to change until one day started passing stools several times a day-with blood mixed with mucus,have past history of SRUS,rectoanal intussusception,mucosal prolapse,weak squeeze pressure(on manometry)now passing motion 4-5 times a day(no relief)soon after coming back from bathroom feeling discomfort something moving up and down between lower abdomen and rectum and loud audible and extremely foul smelling gas)He did repeat sigmoidoscopy which revealed rectal ulceration(biopsy-chronic colitis),gave srfil and mesacol enema,but no help..Yesterday he gave pruease 1mg.While passing motion,i feel rectum is folding outwards and stool moving back.what is the reason?why did doc give pruease inspite of doing surgery?plz answer..