I was having this same issue until I took a look at how Happy Mumsy Year! included her timeline within her outline. I went through and painstakingly added dates to all of my major events, and in the process realized where my gaps in time were. I've started filling in those gaps and it's added many more scenes and details that I never would have thought of before. I've upped the conflict and drama, and I've rounded out my protagonist quite a bit. I still have a way to go (and of course, if my protagonist takes me in a different direction, I'll go there) but I'm getting there!