In that case download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.
IMPORTANT:
Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck's Privacy preference pane so that it can get additional information from the Console and log files for the report:
Also click and read the About info to further permit full disk access.
Copy the report
and use the Additional Text button to include the report in your reply.
Then we can examine the report and see if we can determine what might be causing the problem.