Help! Why there are flies in my bathroom? I can’t get rid of them and more Keep coming help?

A month ago I had one fly inside my studio home. I couldn’t kill it so I left it there. Soon there was two. Now I’m killing 5-10 flies per day and when I kill them, MORE appear. I don't know where they are coming from. Do I use bug spray and spray it on the bottom rim floor of the bathroom? I have. Cabinet mirror on the wall with 6 lightbulbs and the flies sleep there. Maybe the eggs are on that top high shelf? Should I spray bug killer spray on the top shelf and on the bottom rim side of the wall?

Help! Why there are flies in my bathroom? I can’t get rid of them and more Keep coming help?
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