I find humor in the bitter irony that the day I feel the worst is precisely two times my longest fast.
There is a reason for that. It is best not to more than double the prior fast. Hence, you may want to end this one soon (since 14 days should have been your limit), and then do another one later if desired..
If you really wish to continue, then be acutely aware of things like true hunger, hair falling out, etc. as signs to end it..