Boy, it sounds like you've got workout burnout. I often feel like not working out, as I would much rather be doing something other than exercising, but usually once I suck it up and go for it, I consider it a little victory. And yes, there are times I feel sluggish during a workout and it really stinks. I'll try to put my finger on it and think, "Hmm, what the heck is different about today that is making me have to drag myself around the gym?" but often times, theres no clear reason.
If you think consuming some caffeine after dinner won't keep you up at night, I suggest drinking a cup of coffee prior to your workout. I perform better when doing cardio with a bit of caffeine in my system; studies support this. It may serve to get you riled up for a strong walk/run. In addition, how about dedicating two or three nights to weightlifting? I applaud you for engaging in cardio every session but done properly, weightlifting will give you the same heart-healthy benefits. (Not to mention, build muscle to aid in calorie burn.) Then on the remaining days, try to push yourself hard when doing the treadmill work.
I can relate to overeating - I have mastered this skill

. I find that deprivation or substitution does not work for me, though; if I'm having a sugar craving, I go ahead and consume sugar (as opposed to a product containing a sugar substitute). I do sometimes overeat but I feel my craving gets satisfied. I certainly don't want to condone this, and if you are afraid you might be triggered then don't try this: ony you know your next move.
Take care to give yourself a bit of a break, though, somewhere, so that you can ensure you stick to this healthy way of life you've adopted. Now, go drink a cup of coffee!
