It is just another route the toxins are taking leaving your body, perfectly normal.
ETA: congrats on 3 weeks!
Let hunger by your guide though if you are fasting to completion.
Your urine should not be clear, how much water are you drinking? My urine while I fast is usually very yellow.

A white tongue nomoreMS is a barometer of the state of your abdominal intestines......toxic.

Given sufficient time, the white tongue will clear slowly from the edges and become completely clean by the end of a fast that eliminates toxemia.
If food reserves are becoming exhausted, then hunger may return before the tongue clears completely.
The coating on the tongue, or the clearing of the tongue, is not a reliable guide as to whether the fast should be broken: only genuine hunger has that status.

Regards

Chrisb1.