Crap Run!

I don't know what is wrong with me!! I had a good long run Saturday, Tuesday night run wasn't bad (8:39 pace for 9 miles with 90 degree temps and high humidity) overall considering the conditions. This morning I was up and out the door just after 5, humidity is high (my shirt is soaked) and it's not as cool as would be nice, but it wasn't overly horrible. I decided instead of a straight tempo I'd do longer cruise intervals, 2 miles at hopefully 7:45-7:50 and then a mile rest and another 3 miles of cruise intervals and a cool down. My warm up mile was 9:42...very slow for me lately. First 2 were 7:56 and 8:05...OK, not what I wanted but I dealt with it. Had a 9:11 recovery and then 3 cruise at 7:54, 7:59 and 8:10 or something like that. Last mile was around 8:40...Overall was 1:07:53 for 8 miles. NOT a good run with average of 8:30. I need 10 seconds per mile faster than that (OK, technically 6 seconds) for 26 to make my goal 3...this is not good. I have no idea what the problem is. Tempo runs are my least favorite but probably most important....I'm heavier than I want to be...and maybe my eating has been crap...have to stop with the junk and just maintain keeping good food in me...how do I do that though?