down on my luck  -  Some people have ＾good luck￣ and some people have ＾bad luck￣.  When you have no control over how something will happen, maybe everything will happen depending on luck.  If you are experiencing bad luck or if you are having a difficult time, you might use this expression, ＾I¨m down on my luck.￣  ＾Things are not going very well for me right now.￣

I lost my house key and my cell phone is broken.  I¨m a bit down on my luck.

Tom can¨t find a job, his girlfriend is angry at him and his dog is sick!  He¨s really down on his luck!