How to determine if I'm just incompetent, or if my work is more difficult than expected?
let me introduce you to my friend the impostor syndrome. In all likely-hood you are behind but not incompetent. From my experience, almost all people I interact with in academia have something that is past it's "due date". I think you need to take a deep breath and remeber that what you're doing is dificult and you should expect some (if not a lot) of trouble.