So I hit a very serious running confidence of crisis in November 2018 less than 2 months from marathon number 1 and Dopey number 1. It was brutal. In the worst moments, I was actually contemplating canceling the trip altogether at worst or eating the very expensive costs of the race at best.
First thing that helped me was to come here and be honest about what I was dealing with. This forum is where I talk running roughly 90% of the time. Allowing myself to be honest about how I felt actually helped. Instead of spending way too much time letting my fears ping pong around in my head, I got them out. Just doing that helped some. Second thing that helped was consulting with
@DopeyBadger. After a difficult long run followed up by 2 brutal shorter runs, I was a wreck. Billy told me to take the rest of the week off and then slow my pace down the next week as needed. Doing that, combined with real encouragement from other runners here sharing their own versions of been there, done that, and finished anyways helped a great deal. When the next week came, I resumed running and was back in my groove. And though I didn't know it at the time, marathon number 1 has now turned into marathon number 4.
I'm not saying that all crises of running confidence resolve quickly. Some may not.