Overtraining?

Wednesday night runs are usually pretty easy ones for me. Those are the pot-luck dinner runs that are hosted at a different person's home each week and the host provides the route and the main dish. Every one else brings their appetite and a side dish and it's usually a laid back pace allowing us to see different parts of Kansas City and the surrounding areas.
This past one, I was coming off two (relatively) fast runs on Monday night and Tuesday night back to back after running 11 on Sunday. I had planned on doing about 7-8 on Wed nite and since I knew the route, I felt comfortable with it. Starting out, my legs immediately felt like I had done a HARD bike ride that day (which I had not) and took them a while to get warmed up. Even once they did warm up, they still didn't get much energy to them. I was struggling to keep up a medium pace with the lead guys and eventually fell off. I told myself that it was alright and I'd just run my own pace to finish. Didn't happen. After the turn around point, I did one more mile and had to walk it back. Did about 4.5 or 5 miles running and did the final 2 or 2.5 walking! My legs HURT the rest of the evening. So I had to take Thursday off even though I REALLY wanted to hit the newly remodeled Psycho Wyco trails on our thursday night runs. Shane and I want to do 2 laps this weekend at Wyco to get in at least 20 miles of hills, and I think I'll be ok for that, but I'm also thinking about riding Clinton lake on Saturday with the guys from Cowtown cycling. If I do that, I may not have enough left for Wyco on Sunday. I guess all this rambling leads me to conclude that eight years of racing STILL has not taught me how to balance pushing it to get stronger without hurting myself by overtraining. I HATE this because it makes me feel like such a friggin weakling!