In my own experience, alternating between bouts of self-doubt, hopelessness and despair followed by episodes of excitement, mania (the good kind) and progress from the fire of a new idea all seems normal and unavoidable to me. You just have to slog through the rough times and keep going. Don't listen to naysayers and don't give up but be sure to take breaks. Keep a journal of what hasn't worked in the past and summarize what you learned. Just writing it will put it in your subconscious for later use and occasionally you'll want to go back and revisit an idea that did not work.
