Check this out of you have some quiet time.
The Self-Acceptance Project
It's a series of video/audio lectures and discussions on the topic of self-acceptance with practical tips etc. It's free, you just need to type in a name and email address to log in but no need to sign up to anything.
"Session 1: Compassion for the Self-Critic" deals with what you are asking.
Some of the other sessions are very good, too.