Lethargic, tired, and low drive. Any ideas?

I'm not 100% sure why but in the past year or so I've been losing my drive and I've been feeling really lethargic. I may not actually have but I still enjoy a nightly masturbation to help me go to sleep, but for some reason I just don't have the same stuff as I did a few years back. It seems harder to be turned on and it's harder to get an going, I mean I can but it's a lot more work and even then it takes a lot of work to keep it erect. I'm only 21 and 188 Lbs with a little bit of belly fat, other then that I'm pretty lean looking. I haven't worked out in a while either and I'm wondering if it's playing a role in this. I eat mostly rice, peas, corn, chicken, the occasional beef, and no vitamins. There's not much diversity in my diet, could it be a nutrional problem? I usually get around 8 - 10 hours of sleep, sometimes more. Please help me, I really want to get that entergetic feeling back.