I am a 47 yr old female. i have severe abdominal bloating, (colonoscopy showed nothing), pelvic cramps, no menstrual periods for 3 months, and backac?

Several things: At 47 you are in the perimenopause and skipping periods is common. It may well be that the skipped periods aren't related to your backache , bloating,and pelvic cramping. A normal colonoscopy doesn't rule out irritable bowel syndrome which can cause these symptoms. Talk to your PCP, GYN, or the doctor who did your colonoscopy about this.