Self Doubt

Self-doubt has been a major daily issue in my pursuit of this degree. I am tired dealing with this, it is never ending, and even not coumaflaged by the positive words received from my supervisors and the advisory board.....why is well done, outstanding, and excellent are still not enough? Why is with every praise words that I received, I think of the hidden negative words they want to hide from me? This is further compounded by a not too positive feedback that I have been getting for my written english and the content of the recent paper. Even if the feedback had several praise words in between, I succumbed into further self-doubt. How to increase self confidence? I am really lacking of it!!!