How to know if the melody you composed has not been used before?

hello,

I ask this because I am working over a piece and two melodic phrases were composed that sound so perfect and simple that I have the feeling I heard that before, same a friend, but we can't determine where. So I also thought in the possibility that if something is so perfect for our human hearing, it could be recognized by us like familiar. Those melodies are of those that don't need any note to be changed, they sound round and the feeling is logical and with sense, there are several in history, pop music included. But I as I am not sure, and therefore this is still a possibility, how can I know?. I am not going to earn money with this, but I don't want to copy others work.

Please help.
Thanks!

I didn't find the right solution from the Internet.

References:
https://www.youngcomposers.com/t35755/ho...en-used-before/


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