I am EXACTLY the same as the original poster mentioned. I am always so hard on myself, never believing anyone when they tell me that something I did/made was good. I swear I am the queen of self-sabotage. I am trying to change that, but it isn't easy.
I think the hardest part is when I am working on a project, and then half-way through I start to second guess myself and lose track of my original inspiration and plans. There have been times that I just give up, because I've beaten myself up so much over it that I can't see the point anymore.
You are not alone.