Tired after early morning long run

I'm not really a whiner in general, but I'm just tired. Not sick and tired. Just tired. This week was my first real marathon training week. I was supposed to start last week, but was giving an injury more time and took it easy.

I usually get to bed by 10:30 or 11 and naturally wake up (no alarm) at about 5:30 or 6. Wednesday morning I did a tempo run that only had one mile at the goal pace and I stopped after four miles instead of doing 5. Yesterday morning I only did about 30 minutes of weights, but after that I was still sleepy and out of it.

I decided to do my first long run before work this morning. Plan said 15 miles at 8:11 pace. Last week's long run that I missed was for 13 miles at 7:56 pace. I figured I'd try for something in between, maybe 14 miles at 8:00. I started out at about 5am (had to use the alarm for this one) and had a tough time getting to the pace. First three miles were more like 8:20 or slower. Then it got better and I started hitting some low 8:00s and even sub 8 for a couple.

At about mile 6.5 I stopped for a short water and food break. Getting going again was tough, but I fought the urge to go back home and get another hour of sleep. I kept the pace pretty close to target for the next few miles, but after mile 10 I wasn't feeling up to 3 or 4 more. I decided to push one more mile and then walk it home. I ended with 11 miles and an average of 8:08. Not horrible, but not where I'd like to be. I've done better in recent weeks.

Now I need to figure out if this sluggish running and overall tired feeling is due to the heat/humidity, what I eat, the workouts, or something else. It is probably the combination of these. I try to convince myself that I'll see improvements once this heat and/or humidity lets up. but it is frustrating for now. Meanwhile I decided I probably shouldn't try to fit a long run in before work because I'm mostly just trying to stay awake.