I feel pain on the bottom of my spine. the pain increases when i wait some time to evacuate or when i hold gases. what could it be?

Coccyx Pain: It sounds like you have "referred" bowel pain from an overfilled descending colon or rectum. Make sure you are getting enough fluids and that your diet contains sufficient natural stool softeners, such as fiber from leafy green vegetables, and not an over abundance of protein from meats. If that doesn't work, you should consult your physician or a gastroenterologist.

Unclear: Do you have diarrhea? Blood in stool? Pain worse sitting standing or walking? Twisting? Unclear from your question if you primarily have a colitis issue or lumbar spine and disk problem.