at wits' end

at (one's) wits' end (at the limit of one's mental resources; utterly at a loss) — быть в крайнем недоумении, в растяренности; (просто) не знать, что делать, как поступить; стать в тупик

Example 1: I'm at my wit 's end. I have to do something, or this whole situation is going to crash badly.

Example 2: Maria was at her wits' end trying to find supervision for her son, Tom, after school before she returned from work. The neighborhood babysitters were reluctant to provide care because of Tom's diagnosis. (Children Today)

Also
at (one's) wit's end

see also
[at the end of one's rope]
on the verge of a (nervous) breakdown