I made a silly mistake
I took my bike out of my car today and reattached the front wheel. I failed to notice that the brake was rubbing against the wheel. I rode it with the brake rubbing against the wheel for 10 miles before stopping for food, and then I noticed my front wheel wasn't rolling freely. All that time I was wondering why I was going slower than normal, I was averaging 11 mph. There was no wind and it was flat, so I thought I was bonking and needed to eat something sugary. I fixed the position of the brake and that made a world of difference. The next 20 miles flew by and I had an average speed of 15 mph for the trip including the first 10 miles. I feel so stupid after making that mistake. It's like driving with the parking brake on and wondering why the car is accelerating slowly, which I've done before too.