What should I do next if a glycerin suppository does not work?

Depends. On why you are using it. If you are constipated and it doesn't help you poop, then try drinking more water and increasing p-fruits...Peach, pear plum, pineapple, papaya. Peas, pumpkin, pomegranate...If you are severely constipated, ask your doctor about other methods....Increased fiber can help, MiraLAX (polyethylene glycol) can help, etc. You may need guidance for best results.