Not so tough :'-(

Pool running makes my legs feel “better”—however, the strength building it does is one of those deceptive workouts. It doesn’t feel taxing on my muscles or even very tiring, but I have noticed my quads feeling more sore, and kind of thick on my runs.
That said, it was actually better today when I took off for my tempo run. That surprised me—I was concerned about doing a tempo at all with my slow paces and thick legs lately.
However, this was the first workout that I actually quit. I feel awful. I felt ok, though I was going slightly slow, and I really was determined to make it. I told myself the purpose of this workout, even if I couldn’t hold the pace, was going to be to challenge my mental willpower and pain threshold—after all I’ll be hurting like that and worse at mile 20 of race pace!
But I lost it at 4.5m. I was hanging in there, even feeling more positive, when I realized suddenly I’d miscalculated and had 3.5 more miles, not 2.5 [I’d set out on a 6m path when I was supposed to have 7]. Combined with my legs feeling like concrete and feeling about to puke I decided to pull it in at 5m. Even then I clocked slower than my marathon pace.
Now I feel HORRID. Because of my bad run and even worse that I didn’t finish.
I used the excuse that I’ve added pool running and also didn’t take the real recovery days I was supposed to this week [with the excuse that ALL my runs were slow so I could run more], so it was reasonable that I wouldn’t be able to do all the workouts.
I know I made a mistake of not recovering right if that is the reason for today’s flop, but I still feel like I whimped out. After all, every run isn’t going to be “fun” if I want to run at an advanced level.
I should have pushed it with the attitude of a champion and not whimped out like that.

So far this makes for a crappy week, and I’m in a dilemma about where to go from here.
Are the runs challenging simply because I’m in peak training right now?
Or am I overtraining?
Not recovering properly?
Should I change something…or be tough and realize this is part of advance training.
Grr, I feel so lost. :-(