The pattern {noun} after {noun} is a common rhetorical device.

The pain came in wave after wave.

We were having a great time at the pub, singing song after song.

You can think of it as a periphrasis for the plural that conveys the sense of "many" and "repetition" or "continuousness".

Paraphrases of the above:

The pain came repeatedly in waves.

We were having a great time at the pub, singing many songs over the course of the evening.

The pattern {noun} after {noun} is a common rhetorical device.

The nausea came in wave after wave.

We were having a great time at the pub, singing song after song.

You can think of it as a periphrasis for the plural that conveys the sense of "many" and "repetition" or "continuousness".

Paraphrases of the above:

The nausea came repeatedly in waves.

We were having a great time at the pub, singing many songs over the course of the evening.

or

The nausea came in waves, one after another.

We were having a great time at the pub singing songs, one after another.