Now What?

It's been almost a week since the 5K, and already I feel as though I'm losing my stamina. I took 3 days off because my legs were SUPER sore, and on the 4th day back, the run was very challenging...3 days felt like 3 months off. It's crazy how quickly the weight goes back on, the stamina is lost, the muscles fatigue. Today was my second run of this week, and I could only manage a 10 min. jog, 3 min. walk, 7 min. jog. I'm not even near ready for the first week of the 5K to 10K app. At this point, I know it's all mental. I have only once ran a whole 5K distance (on the treadmill) without walking, and question whether that needs to be my next race goal versus a 10K. I just don't feel that I'll be ready for a 10K by Thanksgiving. Do I go back on the Couch to 5K app and start again at a higher pace (my jogs have been at a 4.5mph speed)? Or do I forge ahead with the 10K training plan? I know for me, I need a training plan and to register for a race to keep me motivated...I find it hard to mindlessly continue to exercise without a fitness goal. Any thoughts on what my next goal should be?