The first thing you need to do is visit a doctor because he/she can help you quickly identify your problem and give you personalized and credible advice.
But if you don't think it's serious enough, it sounds to me that your body needs a little more healthier food and more exercise. Do you live in the city or somewhere with pollution? Maybe it's the air in your home. Try buying an air purifier and make sure you stay away from any perfumes in your home! Pumping chemicals through your house to make it smell better is not good at all.
I would stay away from Listerine, too. It can also kill good bacteria that prevents diseases (source: http://www.sciforums.com/Is-Listerine-Good-or-Bad-for-you-t-61518.html)
As for flossing, try to remember to do that twice a day because it can help prevent heart cancer, not that it will do much to help your short term sickness.
Vacuum every other week, and use a wet cloth to dust. Old dusters just move around the dust.
But the biggest problem that you seem to be facing is an unbalanced diet, infrequent exercise schedule, unfit environment with something wrong, or lack of sleep. In fact, sleep might just be the answer.
Do you have an infection? People who have infections often times feel awful for no apparent reason. This may be it, because I remember feeling cruddy for weeks before finding out I had an infection.
So check and double check all the factors for good health (diet, sleep, environment, excess stress, exercise) and talk to your doctor.
Hope you feel better!
Personal reference, http://www.sciforums.com/Is-Listerine-Good-or-Bad-for-you-t-61518.html, health classes, research done for my website http://www.thenearbyfuture.com 's health section.