What Causes Bowel Movement On Taking Norco Pill?

Hello. I take Norco 3 times a day for back pain. I take them every 4-6 hours, (two 7.5).. About 45 minutes before I took them I ate a few slices of pizza. About 15 minutes after I took my pills, I had to defecate. I waited another 45 minutes, and the pain didn t go away. Did I poop them away? Should I take 2 more? I also know from the past that if I don t wait 4-6 hours, they don t work as well. This has happened before