I'm having similar issues. It took a good long look in a full length mirror before I was convinced that I needed to go out and buy new, smaller jeans, and even now I don't want to throw out my old ones, even though they are now two sizes too large. For me at least, I think part of me is worried that I'll need them again when I suddenly wake up tomorrow (or next year) and I'm my old size again. It's like how can looking and feeling this great possibly last? Plus, those pants cost a lot of money, and the new ones I buy cost money too. AGH!!
BUT!! Fortunately I have a good friend who knows every consignment and thrift store in a hundred mile radius, and she took me to a couple of really nice places that specialize in nicer, more "modern" clothing (I'm sure you know how sketchy thrift store clothing can be) and for the first time in my life, I bought a pair of jeans that fit GREAT!! And for only about $11. So completely worth it!!
I'm still not willing to toss my old jeans, but I've managed to part with a lot of my larger shirts. But my advice is to at least go out and treat yourself to some things in your new, smaller size. Get them cheaper at consignment stores if you're like me and planning on going down another size. You can always donate them again later. It's amazing how incredibly smokin' hot you feel in smaller sized clothes that actually fit!! Great motivation to get down to the next size!!