I finished my first Olympic distance tri 2 weeks ago and thought my fitness was going well. The only major race I have the rest of the season is the Army 10 Miler on October 4. Problem is even though I was running close to 7.5 miles a week in July, I am now having issues managing 5 miles without hitting a major wall.

I am wondering if one or all of the following are factors:
1) The heat, I live near DC and it has gotten hotter in the last few weeks
2) I have lost 8 pounds this summer and I am wondering if my body is bothered by that
3) I have pushed my body too hard

On top of all of this I have a friend wanting me to ride a metric century with her 3 weeks before the Army 10 miler and I am having issues deciding if I should. I am worried if my body is this tired now, if I do the metric century I will never be able to do the 10 miles.

Please help!