Crappy mid-week long run

Today was the longest mid-week long run I have ever done. It was a 12 mile one. Although I had set my alarm for 5:30 AM I goofed and it was set for 5:30 PM so I awoke with a start at 7 AM. Yuck, this meant I was going to be late for work. When I woke it was 74 degrees F (what?!), hot and humid. The streets were wet with rain. I headed down Metric to Research, and then another mile on Research. I carried water and a Clif Shot. On the out segment I was running into the wind. I also seemed to be always running uphill. Ugh. Midway I had finished all my water and downed the mocha Clif Shot at 6 miles. Part way home I stopped at a gas station to refill my water. I finished the run, but it was a struggle. I was soaked with sweat. This is not getting easier, and I’m supposed to get stronger, but I just feel weaker. I was probably doing 10 minutes/mile. Bottom line, it was a crappy mid-week long run. I keep reading about my coach and how he’s just running smoothly and consistently. What is wrong with me? Why is it so hard?