My week ay runs have felt terrible

I am training for a trail half marathon, and my long runs on Sundays feel absolutely amazing. I feel energized the whole time and so fresh and light. Then it comes to my shorter weekday runs. This past week they have felt terrible, I feel done with the run at 1 mile, constantly checking my watch and feeling tired. What gives? Why I am having this fatigue during the week but then doing so well on the weekends? Any way to push through this feeling during the week?