I think what Thunder Bow was trying to say is that you need to explore and challenge your core negative beliefs.. This is the very thing which Cognitive Behavioral Therapy is about - strategizing and developing ways to challenge these thoughts and come up with alternatives. It does take a lot of work - most programs and books are designed around a 12 session format. I myself found this to be very successful.

Have a read on 'Cognitive Distortions'. There's lots out there on the subject; here's one that includes some great resources: http://psychology.tools/cbt.html

If these 10 Distortions ring any bell with you it might be worth doing some CBT work - which you can do on your own (but that's an entirely different post).