No matter how you love your job, there will always come a point in your career that you get burned out or exhausted. It seems like all your energy is sapped and your motivation gone out of the window. It's a normal part of life so don't worry. All you need is a little self-encouragement that will get you kicking again in a short while.
Everyday work doesn't just involve your physical body but your thoughts and emotions as well. Establish a momentum for these three factors as soon as you get up from bed in the morning because these three will be the basis of how your day will start and end. Boost up your mood through exercise and a good breakfast and start the day with an optimistic outlook.
Whether you admit it or not, money is the number one motivation why you work hard so let it motivate you every time you're feeling down and discouraged. Look forward to the reward you are going to collect at the month's end and start imagining the things that you are going to buy your money with.
Having a competitive mindset will also help you see things in the office more differently. Instead of just being a mediocre employee, spur yourself up and do your best to be the best among the rest. If you are given two projects for the day, try to finish four or five. It's okay to have a friendly challenge with your co-employee once in a while. Your boss would even be happy to see you deliver more than what you are expected.
Look back at your achievements at the end of the day. That would surely hype you up and encourage you to work harder. Humans have a tendency to perform better when they are being praised for their accomplishments so don't forget to give yourself a tap on the shoulders and say, "Good work!"
Not all of us are given the opportunity to do what we really love to do. So if you're working on a job right now that is not actually your ideal job, don't lose heart, consider your situation as a stepping stone. Who knows, maybe by getting yourself motivated to work hard and deliver more, you might get recommended for promotion!