I just couldn't concentrate.
  Lots of things would come to mind. Revenge, sex, regret, 
  frustrations, hope, plans and a lot just used to happen in
  mind at that time. More than usual. More than it would
  usually come to my mind.

I'm only just beginning to learn about meditation but in most forms of meditation these thoughts are perfectly normal. Mindfulness meditation stresses that these thoughts are okay. One of the first things you learn is to accept these thoughts without judging them or judging yourself.

If you ever give it another try, give your mind permission to go wherever it likes. What will your mind feel like when you're not fighting with it and trying to make it think (or not think) about particular things? It may be rewarding to find out, or at least relaxing.

Best wishes!