My problem is I just do not enjoy exercise. I grant that some level of exercise is probably healthy, but I just don't enjoy it. At all. Not long ago I made myself run 3 or 4 days a week, for about 4 months. I did build up my ability to go longer distances but it never made me feel any better. After running I never felt energized or more productive; I felt tired and wanted to go to bed. I had similar experiences with strength training, tennis, raquetball, cycling... I don't think you can form a habit out of something if you don't enjoy it. You can keep doing it out of sheer willpower, but it will never become a habit.
I used to hate working out, specifically because I absolutely hate cardio (looking at you treadmill, running, walking, biking, elliptical) but I found great joy in lifting. I started off slow, but even now I can really get into it.
I look forward to going to the gym and getting a work-out in when I get home from work. I used to absolutely hate it, because people told me that I should do cardio to lose weight ... now most of what I do is lifting. A little cardio and the inches keep coming off, and I keep getting stronger.
Find something you enjoy doing (I love swimming) and find pleasure in doing that, even if it is for a short period of time per day. Running clearly isn't for you, and it isn't for me...
Of course you are tired after you exercise. But a day or two later you should feel more energetic, after sleeping better. You have to do the sleeping too. And eating well. Don't pile on greasy calories to feed your exercising body, that will drag you down more as you eat note. It's all synergistic.
