Perhaps set aside time from 8:00-8:30p for self-doubt. If you find negative thoughts recurring throughout the day, remind yourself that there will be plenty of time to deal with them at 8:00p.  Another variation involves limiting negativity to a very specific location. Research has shown that anxiety can be lessened by limiting it to 30 minutes a day only in a "worry chair".  After your worry session is over, clear your mind by performing some breathing exercises and meditation.