(there's) no rest for the weary
One must continue to toil or work regardless of how exhausted one is. A logical variant of the original phrase "no peace for the wicked." Parents of young children know all too well what it's like to have only a few hours of sleep and still have to get up at the crack of dawn—no rest for the weary, as my granny always said. There won't be time for a break, because we'll need to get going on the next phase of the project as soon as this one is done. There's no rest for the weary!
There is no rest for the weary.
Prov. Even people who are worn-out must continue to work. (Describes a situation in which a tired person has to do more work.) By the time I finished doing the laundry, it was so late I had to begin cooking supper for the family. There is no rest for the weary.