Hi! My only thought was if you were on any meds that may make you tired? Otherwise, I would check with the doc just to be sure.
I know what you mean about the exercise. I just FINALLY got back into routine. I get up every morning & exercise before work. I've been going for 4 or 5 weeks straight now, and I feel really good! But it took me a while to get motivated--I hadn't worked out since last July. I tried a few times to get back into routine, but I'd exercise maybe 1 or 2 days, then not again for a few weeks. The first week is the hardest, then it's a breeze--at least for me anyway!
Oh, and I do notice that I sleep better when I exercise.