[Misericordias]

Hello, I am currently doing homework for my Japanese class, and this phrase is giving me quite some difficulty. The sentence is:

お医者さんによって、”まったく素人の話はわからない ”。

I translated as such:

When the doctor left, "Geez, I don't understand why the doctor can't speak like a normal person".


To be blunt, I have no idea how to translate によってas I have no idea what it means. Also, I am not sure I translated the second part properly. Any help would be much appreciated!