Had A Rectal Tumor Removed,and Had A Colostomy 4 Weks

Had a rectal tumor removed,and had a colostomy 4 weks ago. Kept getting bad spasms rectally so they prescribed 10mg valium suppositories. They say they won't constipate, also was and still am taking pain pills. Using fiber and had no problems with bowel movements till I started the valium last week. Is it them, do I need to take more fiber or maybe a senn or 2 nighty. thanks for your help. Rick