Day after day and Everyday

Day after day adverb - For an indefinite number of successive days.

Everyday and day after day are semantically related. In some cases you can use "Everyday" instead an adjective phrase "Day after day".

Everyday adjective - Being of the type that is encountered in the normal course of events.

Day after day and everyday are semantically related. Sometimes you can use "Day after day" instead an adjective "Everyday".