Just my experience...
Have you looked at how you are eating? Stress levels? How much sleep are you getting? I went through a brutal fatigue earlier this year, and felt similarly. Just getting out of the car was an effort. Working out? Only because I had a partner, but my heart wasn't in it, and I dreaded getting out of bed to do it. Personally, I had candida overgrowth, but other folks recommended adrenal fatigue, too much sugar in my diet (which for me playing into candida), not enough sleep, and way too much stress.
Since getting all sugars out of my diet, getting 7.5-8 hours of a sleep a night, and working on my stress levels (still working on this), my energy levels are significantly better. I was a Primal eater -- with fruit, dark chocolate, and my weakness of ice cream a bit too often. Cleaning up my diet and focusing on protecting my energy inducers -- sleep, relaxation, time -- I've been much, much better.
All that to say, it probably has less to do with your food than other factors, but take a close look at all of it and see what might be at fault for this. Because you are right to question it -- it shouldn't feel that way. I do half hour workouts that are heavy, intense, and I feel great afterwards -- but I didn't used to feel that way.
Hang in there.