prey on (someone's) mind

Translations
тревожить (чьи-то) мысли
The problem has been preying on his mind for weeks.
Эта проблема тревожила его мысли в течение нескольких недель.
Definitions
To continuously occupy someone's thoughts or cause them to worry or feel anxious about something.
Words
mind

noun
ум
prey

verb
охотиться