I don't think memory is the problem either since the report does not indicate any memory overload after 7 days of use. While performing an intense workload you can check the Memory tab of Activity Monitor. If the Memory Pressure graph is showing Yellow or Red, then you are borderline on memory or running out of memory respectively. If the graph is green and the Swap and Compressed memory values are not in GBs, then you are fine with the current memory. If the Swap & Compressed memory is in GBs, then you may need more memory or you may need to close unnecessary apps while performing the more system intense workloads.
I agree with @den.thed that the internal hard drive is either worn out or actually failing, plus the i3 CPU isn't helping. You can check the health of the hard drive by running DriveDx (free trial period) and posting the complete text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar. Most hard drive issues will be revealed in the hard drive's health report, although there may be some performance issues that will not reveal themselves this way. For a hard drive, usually any "Warnings" or "Failure" notices indicate a worn out or failing hard drive respectively.....a worn out hard drive can be just as bad as a failing hard drive.
