Can't get flies out of bathroom?

I have little flies in my apartment bathroom...they're bigger than fruit flies but smaller than like horse flies, so I don't know what kind they are...drain flies maybe? I don't know where they're coming from. They aren't in the sink, but they will fly around and sit on the mirror, on the sink... show more I have little flies in my apartment bathroom...they're bigger than fruit flies but smaller than like horse flies, so I don't know what kind they are...drain flies maybe? I don't know where they're coming from. They aren't in the sink, but they will fly around and sit on the mirror, on the sink counter, on the wall, in the tub, etc.

The bathroom is pretty clean...it's not dirty or anything, so I don't understand why they won't go away. They're very hard to kill because they fly away so quickly when I try to smash them.

I tried putting yogurt in there because I read it can help attract them all to one spot, which it did, and I was able to kill a few, but there's still more.

I don't know what to do. Please help!
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