головная боль {n. phr.}
golov`naya bol'
sth. that needs to be done and is bothering your mind;
the work that looks as got stuck;
the persisting problem or issue that is not going to be resolved.
See also:
pain in the neck
pain in the ass
Российские автодороги — это головная боль всех водителей. — Russian roads are all drivers' pain in the neck