As a quick fix you can sudo apt-get install python3-pyqt5
But for the sake of your question. Does this happen with any package?
Can you try installing any of the following just to see if it works, these are just quick examples.
pip3 install numpy==1.18.1
pip3 install pandas==0.25.3
pip3 install pep8==1.7.1
pip3 install pika==1.1.0
One reason could be that PyQt5 is to be used with python 2 and hence might only work with pip install PyQt5
