[Japanese->English] いつの間にか with a question?

I have a question about the lyrics of Frieren's OP. This part in particular:

同じ途を選んだ

それだけだったはずなのに

いつの間にかどうして

頬を伝う涙の理由をもっと

知りたいんだ

If i am understanding it correctly, the part after いつの間にか is one running sentence. It is also a question. I believe it means the following:

"Why do i want to know more about the reason that tears were rolling down my cheek?" (not a 100% literal translation. Also "my" cheek is implied here. But it's not important)

How does いつの間にか fit into this? From my research, this expression can not be used with a question, so it does not seem to make sense here.

Is the sentence not actually a question? Is どうして only there for emphasis? Does the sentence actually mean the following?

"Before i knew it, i wanted to know more about the reason that tears were rolling down my cheek"