Mavericks 10.9.5 RAM problem and performance problems
I had exactly this same problem upon upgrading to Mavericks. Unfortunately, you're going to find that 4GB is on the knife's edge of barely being able to run the system at all - note how you already have compressed memory despite not running anything.

Apple needs to be smacked around for this, but unfortunately, it is what it is.

The first thing you need to do is put more memory in - I would go for 16 unless you absolutely can't afford it.

An SSD would help as well - I find that the IO performance on spinning drives has been getting worse and worse with every OS release.

If you can only pick one of these, get the SSD first. You'll benefit a lot more from the IO boost than the memory boost, at least in the short term.