Wow, this is so me. I've literally thought all of these things, but never said them out loud until I read your post.
I have literally told myself I was a loser and worthless over and over and over until I believed it. And now, four years later I've made myself numb with all of the self deprecating thoughts that I feel lost trying to piece my life together.
I have been in therapy for a couple of months and it's helped tremendously. I also keep a word document of positive thoughts. Just any good thing that happens or reasons why people love me and I love them. When I get into a really low mood, I open it up. I read all the way through and it helps to calm those negative thoughts.
Sending you lots of hugs