Hey there,
I feel for yo, i get that, I sometimes feel like I'm always tired, but you honestly, unless it's a medical problem (you should go to the doctors just in case-have you been needing to urinate a lot?) you just need to tell yourself to do it, you can get your energy levels up, also i find talking to people helps me focus and get on with work- call Samaritans they're really nice to talk to, and can help relieve stress, so let it out, and it should make a difference,
xxx