How can I regain interest in things again?

I used to be really interested in Paleontology, Zoology, Marine Biology, Oceanography, Meteorology, Geography, Astronomy, the Revolutionary War, and the American Civil War. I also would listen to classic rock for long periods of time as well. But over the past couple of years I feel as if I've lost interest in everything, and just can't read about those subjects I mentioned anymore. When I do watch a documentary about them I do not pay any attention to it and when I try to read about them I don't understand them. I feel like I just have no interest in those subjects anymore. Also I'm at home 24/7 and I rarely get to go anywhere at all, so I hardly ever get out. I want to be interest in those subjects again like I used to be. What do I do?