nicoleb hit the nail on the head.
every time you turn on the tube (the biggest/worst trigger), open a magazine, look at a sales flyer, go to the mall, etc. - you are interacting with a corporation. The corporation's sole purpose is to make you want want want so you will buy buy buy.
They do not care if you like it, if you can afford it, it if looks good on you or will keep you warm or if it will bankrupt you (literally). These organizations do not have your best interests at heart. And they have billions of dollars at their disposal to figure out the most effective ways to manipulate you.
Turn off the tube, don't go to the mall, etc. etc. If you don't believe what i say is true, i challenge you to simply not watch tv for a month and observe how you feel, your reactions, etc. at teh end of the month. hunter-gatherers had/have plenty of time in which to sing, talk to the family, weave, sculpt, paint, and memorize incredible amounts of song, philosophy, history because they focus on obtaining what they need and when that is taken care of they move onto something else.
you can bake cookies, read a book, talk to your neighbors, go on a walk, draw, sew, on and on instead of shopping. there are also plenty of ways to enjoy clothes besides shopping - learn how to do your own alterations, how to sew for yourself, perfect your photography/modelling techniques for those WIW pix, make up challenges for yourself (SYC for loox based on a blogger or YLFer you admire, do an all-pants week, or an all dress week, no-repeat month, etc.). you can take a local class on graphic design or color theory if you want to blow your mind about putting outfits together (or do your own research online).
obviously this is a topic i feel strongly about. novelty is fun and we need a certain amount to keep mentally and emotionally healthy. but it can get out of balance if you can't feel happy and content without something new all the time. for me, i don't want and don't like to feel controlled by those types of forces and urges coming from outside of myself. meditation is the main thing that helped me see into this and not be so driven by it. good luck!! steph