This happens every summer (incoming college senior). I get home and start my "easy" summer runs. One workout a week, 40 miles/week so far, planning to move up to 70 in August.
3-6 mile, 7:15-7:30 pace runs are hard to complete and just destroy my legs. If I try to do an easy 3 mile shakeout in the afternoon I feel trashed and can barely get under 8:00 pace.
All my workouts so far have been cut short, by me, halfway through. I can only give it an honest effort for about 5 minutes. No matter what pace I'm supposed to be running (5:50ish or 6:10ish depending on the workouts so far), that particular pace is forced and awkward to run at.
Everything feels wrong, there is no "rhythm" to my running anymore. My knees hurt, my feet slap the ground, my arms feel somehow too long and don't just do their own thing, I have to consciously move them forward and backward and my shoulders hurt. My quads lock up about 2 minutes in to any sincere effort to run fast (sub 7:00 pace).
WHY? It's not that hot yet. I get enough sleep. I put in less hours doing other stuff than during school. It doesn't make sense to me.