How can I tell if my MacBook Pro was hacked and how do I fix it?

About 10 minutes ago I tried to log into PayPal and I got a message saying my account was temporarily blocked because I tried to log in too many times. Problem is I only tried once now and once about 3 hours ago (it was fine back then).

Then I visited another website I am usually logged in (guru.com) and I found I was logged out for some reason (the last time I visited this website was yesterday and everything was fine.)

The same thing happened now with my Apple account as well as my Gmail account. I am usually logged in on both and now I had to type my password again.

I went to Facebook and it was fine, still logged in.

How can I find out if my MacBook Pro was hacked and how can I fix it myself? In case it matters: I don't have any third-party antivirus program installed.

Thank you