not one's day, this is
not (one's) day
A day that has been particularly stressful, difficult, disappointing, or filled with unfortunate events for one; not a good day. I can't believe I got locked out of the apartment. This is just not my day. I'm sorry, sweetie, I know you studied hard for that test. It just wasn't your day.
See also: not
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
not one's day, this is
Also, just one of those days. Nothing is going right for one today. For example, The car wouldn't start, it rained unexpectedly-this is not my day, or The phone has rung nonstop all morning; it's just one of those days. [c. 1920]
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.