there are a number of signs that your body has finished the detoxing and eliminating process by well defined markers and these are......................
The Breath, which during all or most of the fast has been offensive, becomes sweet and clean.
The Tongue becomes clean. The thick coating which remained on it throughout most of the fast vanishes.
The Temperature, which may have been sub-normal or above normal, returns to exactly normal, where it remains.
The Pulse becomes normal in time and rhythm.
The Skin reactions and other reactions become normal.
The Bad Taste in the mouth ceases.
Salivary Secretion becomes normal.
The Eyes become bright and eye sight improves.
The Excreta loses its odor. The Urine becomes light.
The primary indication that the fast is to be broken is the return of hunger; all the other indications are secondary. Often one or more of these secondary signs are absent when hunger returns, but one should not refrain from breaking the fast when there is an unmistakable demand for food, merely because the tongue, for example, is not clean. Inasmuch as all the signs do not invariably appear in each case, do not hesitate to break the fast when hunger returns.
In addition the pains you are experiencing on day 21 are most likely effluent material being deposited in your stomach from the Liver such as bile, left-over stomach acid and so on which in some cases is the cause of nausea and vomiting.
also has this to say.......
"Increased peristaltic activity of the stomach walls, due to "nervousness," may also result in discomfort that is mistaken for "gas pains." Increased tension may occur in any section of the tube and thus pain or discomfort may be either general over the abdomen or may be more or less localized."