Hi,
Maybe some positive affirmations would help you to manifest positive thinking. Acknowledge any negative thoughts that challenge your beliefs but don't hold onto them, merely acknowledge them and then let them go. If they won't go then distact your mind.It might take a few goes, but it will begin to work. Thoughts can become habitual if we allow them to and cause anxiety, it is just a matter of retraining our brain :)
Gentle Blessings
Helen