Here's an idea that might help.
G_STRING,
I think Whirly has answered your question superbly. I too have the same problems that you have and am working on them in much the way Whirly has suggested. Nevertheless, I think I'll print off Whirly's reply and refer to it every time I get dispirited.
Here's an idea of my own, however, that has helped me and just might help you with your navigation. One thing that has always unhinged me has been to find, when airborne and miles from base, that there is some item of my navigation planning that has been either missed or else done wrong. I now have a procedure of my own that prevents late discovery of errors and omissions and also prevents me from distrusting my own flight planning.
As you know, there are many elements that need to be planned prior to flying. Notably the completion of your flight planning form (working out MSA, magnetic heading, distance, groundspeed, etc) and inclusion of the various items on your chart (eg, track-lines, w/v arrow etc) in preparation for a flight.
What I have done is to produce a checklist table for all these elements, adding in a gross error check at the end, to ensure that all my calculations are correct before flying. I have put this inside one of Snowpake's stiff 'Showcard' display laminators and bonded this to the inside of my FB4 kneeboard with double sided adhesive tape.
On completing my flight planning, I go through the checklist, ticking off each item with a fibre-tip. When I am satisfied that my checklist has been completed satisfactorilly, I then wipe the ticks off the Snowpake Showcard with a bit of meths on some kitchen towel so that it is ready for use again.
If you want a copy of my checklist table, send me an email address and I'll send you a copy as an attachment.
Broomstick.