Bowel disorder after ileostomy reversal

After having an ileostomy for 7 years, I had to have a reversal in order to repair a hernia at the stoma site.  Since then, I have had watery diahhrea and my rectum burns with each trip to the bathroom, which is at least 8 times per day.  I have spoken with the doctor who has prescribed pain medication and has told me to apply a topical (nupercainal), however these are not helping and are not meant to address the problem but only mask it for a short time.  The pain I experience each time I empty my bowels is almost unbearable.  How can I get a solution to this problem?