1) I had to straight up relearn to run in those first couple miles because I didn't have that turbo boost I'm used to with (what I'm assuming to be) glycogen stores. And it seemed like I had no energy when I clearly did...
Just make sure you have plenty to help rule out that is the issue. I kept assuming it wasn't for the longest time and now I always start there. It's unintuitive, but more frequent than expected