caffeine intake is only a temporary solution. it only keeps you alert, awake and active for the moment. one reason could be that you stressed out your self or didn't get enough sleep the previous days and its only taking toll now. Another reason could be you have too much sleep or have inactive lifestyle. i suggest you do more physical activities like exercising or just walking or doing house works, because doing nothing can actually be tiring too. our body needs good oxygen circulation to power up our muscles. a good daily vitamin consumption is helpful too. (not just taking about manufactured drugs) a healthy diet can keep you going.

use cold water to wash your face and go out for a walk ,maybe better~

Yes, coffee is a good option which I have regular dosage... Another way is to keep yourself busy that you don't have the time to think you are tired.

Tiring can refer to physical state and emotional state.of course,they both interact with each other. let me talk about my own experience,I can't live without meat everyday,otherwise,I would lack of energy or power.so food is one source of my energy income.second,human has their emotional energy flow,we also have peak emotional state,for me,I can obviously feel i'm super energetic at around 6:00 p.m.So I always deal the most tough thing at that time. but in your case,it happens at normal people life all the time,I always hear people complain like that way.only a few word I wanna add,your life is boring,or r u too lazy?maybe you should set up a big goal for your new year resolution,and work on your cravings.