Anxiety and running

So I’ve been running with some kind of consistency for the past two years now. I would think that I would feel comfortable whenever I knew I was going to for a run. But that is not the case. Every single time I run I think I am going to fail or I doubt my abilities. I just noticed on my Polar Heart Rate Monitor/Running watch that I have run over 250 miles since May of last year. It may not be a lot compared to a lot of other real runners, but it is more than I ever thought I could. And maybe that’s where this anxiety stems from. For 28 years I never had even a thought of trying to run for long distances. The only running I would do would be on a basketball court. Must be just force of habit to think that I cannot finish? Over the past two years, I have constantly pushed my limits with running. In 2008, my goal was to run a 5K and I was successful. In 2009, my goal was to run a 10K and maybe longer. I was able to get up to 15K in training, but couldn’t run the 15K race because of the damn H1N1 flu...grrr. And now this year...the marathon. I AM going to finish it in October. But till then before every run, a tiny part of me doubts my abilities to finish the training session. Whether it is tempo run or speed run, I am just not fully confident in myself. It is a very odd feeling. Normally I am confident in my life, but running constantly makes me question myself.

What do you think of this? Anyone have any suggestions or tips?