Together with WAUNYO, you can also do use the Virgo mantra and/or do a Mercury square, as Virgo rules is associated to all problems with the intestines and the digestion. Mercury rules Virgo.
A good time to start the working would be with the moon in Virgo (for WAUNYO and the Virgo mantra). The moon waning will be in Virgo starting December 21st at 6:51PM (Italian time).
You can also use that date to get rid of any illness, disease and any health abnormalities, as Lydia says in the following post made yet for another day when there was a waning moon in Virgo [Oct 26th]:
Zodiac Mantras: A good time to start a Mercury square would be Wed Feb 8th, as Mercury will be in its exalted sign of Aquarius. If you want to start it earlier, I would recommend at least waiting until it exits Sagittarius (its fall) and enters Capricorn, which will happen this Saturday. At least, wait until Wednesday, though.
Starting a magickal square when the planet is not in its home or exaltation, will still have effect, but it will be weaker compared to starting it when the planet is in its home or exaltation. Also remember that Mercury will be retrograde from December 19th to January 7th included.
These are my two cents.