My Dad Is Having Problems With Frequent Bowel Movements, Sometimes

My Dad is having problems with frequent bowel movements, sometimes 5-6 times a day, gets cramps has to run quickly to get there and sometimes there is nothing, other times diarrhea or just a hard lump, he often does not get there in time. This has been going on for a couple months getting worse and he feels weak. Has had a colonoscopy within the past year and he thinks they said some diverituclitis at that time. Doctor increased his antidepressant thinking it is nerves.