I have some trouble with that too, best thing I have is to make up a list of reinforcing statments about yourself. Even if you don't fully believe them say them out loud 20??? times a day, write them over and over again even. the hope being, that you can believe in the statements and reminds yourself that you are looking too negative and that there ARE positives.
Just having a physical reminder might help

sorry that I don't have more advice,
also,

to PC