Every writer runs into this, generally in every single book. The middle. It lurks between the beginning of your book and the exciting conclusion, and its mission in life is to Atreyu you right down into the yucky, mucky mire in order to prevent you from ever actually finishing.
The Great Swampy Middle (or GSM) knows no fear, no mercy, no regret. It doesn’t come after you. It darned well knows that you’re going to come to it. It knows that you’re going to be charging along, sending up the spinning plates, ripping out the strong character introductions, planting cool bits into your story for the future, and generally feeling high on life. And just then, as you get all that fun opening-story stuff done, it pounces. And suddenly, you’re staring at a blank word processor screen trying to figure out how to get your story through the next paragraph.