Slow and steady heals the heel, but doesn't win the race

I've been in the new orthotics now for 3 weeks. I think I'm getting better, but maybe that's because I'm just not running much. I've averaged like 2 runs a week, and I feel like I'm getting slower and slower. This morning I was struggling to keep a 10 min mile pace. Maybe I'm tired from the weekend? On Saturday, I did a 50 mile ride with the AMC that was pretty hilly. I was dead tired at the end. Also pretty discouraging, since 2 years ago I was doing centuries. Maybe it's a good thing I have to work and can't do the Trek across Maine this year. If I was that tired after 50 miles, how would I manage 3 days in a row of 60+ miles? I feel like I'm working harder, and yet have nothing to show for it. I weigh more, I hurt more, and I'm slower.