Many of us say that we only work to pay the bills, but it is a fact of life that the majority of people have no choice but to work, so it makes sense to try and make the most out of it. Working long hours or for little money can easily make you disheartened, but you should always have a goal you are working towards and keep that in mind.
If you are not happy in your job at present, then try and work out what it is exactly that you are not happy with. It may be that you feel unappreciated, or that you cannot cope with the job load that is being put on you. You may find that by having a quick conversation with your manager, you are able to rectify the situation and improve your job satisfaction.
Always try and further yourself at work by doing things that challenge you a bit and make your mind work hard and always ensure that you get enough down time away from work when you can just switch off and think about something else. If you are happier at work you will probably find you are happier in general.