I thinked I have been hacked

Hi!

I am wondering whether I have been hacked. Some time ago I noticed that my desktop background changed itself. When I tried to change it back it just kept changing to or three times after rebooting and then stopped. (I think it happened once or twice after that.) I saw it might be nothing and left things as they were and did not have any more problem.

About a month ago my pointer stared moving by itself. I tried to redirect it but it didn't work, I could barely influence it. It opened my mail and a few other things and I force quit. It happened again, I force quit again and the next morning everything was fine. Since then everything seemed okay, although I often leave my laptop on without checking it. Today I was listening to a podcast from a USB, I was online and I noticed it was happening again and had opened a window document. Is this someone exterior using my computer? What should I do to check that and remove "him"? I have checked that nothing is shared (screen, etc.) Nothing was. Grateful for any answer concerning this. Thank you.