One piece of advice I got from a manager around interviewing was to be trying to interview somewhere every 3 to 6 months. He's incredibly happy in his role but he interviews to a) find out about new opportunities/products/technologies but b) so that when he finds that one job he really wants he is well versed and ready to nail the shit out of the interview.
You're clearly a smart guy. Do a little study on interview techniques + up the volume of interviews (plus reduce the stress/emphasis on any one interview) and I think you'll surprise yourself with how great you really are.