Hmmm. Well, how's your diet? Sometimes there can be a dietary/health reason involved. Have you done any bowel cleansing or liver flushing? That may help a lot but might take a couple months to se results. Also dehydration could be a factor (recommend reading about the "water cure" on this site.
That said, I don't know if this is helpful or not but i have read that it does help if you can spank the monkey beforehand. Not always the easiest or most convenient option, I know. Do you excercise a lot? That might help too.