It sounds like you have your environment misconfigured in Qt Creator - .h files are only used in C/C++ of course. I don't use Qt Creator for python work so I don't know what you need to change.

And I think you should be using "pyuic5 -x yourfile.ui -o ui_yourfile.py" as a command line. The usual convention is to name the output file the same as the input file, with a "ui_" prepended to the start. This makes it easy for you to keep track of which ui and py files belong together.