I second what SeguaceDiSatanas said; I don't think it's an issue of endurance. Doing things against your will or that you have no interest in is a form of depression, as the flow of energy is impeded.
Something a lot of people don't understand is that you don't "get" energy to do something; you generate it. Kind of like you can wake up full of energy and walk into math class and be instantly depressed. Or you can be completely "exhausted," and something beautiful happens to you, and you feel your whole body vibrating with energy for the rest of the day.
You simply lack sufficient interest in these activities; that's why you feel the way you do. If you could talk about something you're really passionate about, I bet you could do it all day, not just for 3 hours. You wouldn't feel tired at the end either, certainly not the same way you do now.