Over training is very common amongst us older folks but hard to recognize, and hard to let go of our need to stay in shape or chase our youthful conditioning that will never really return. Try a couple days off with some Yoga as suggested above or just a couple days off doing no exercise at all and see if your energy doesn't return. It seems like a step backwards but think about any pro athlete in any sport. If they can arrive at the playoff's 'rested' that can be a huge advantage.