Lay down here on my couch for a little retail therapy, if you please. We're going to have a discussion about shopping. Actually, I'm going to get on my soap box, but feel free to return fire if there is anything about this subject you'd like to discuss.
First of all, never, never, never ask me (your friendly sales person, notice how I put sales in bold?) if an outfit looks good on you. Please don't put me in that position. Take a friend or your partner shopping with you if you want an honest opinion, but please don't put me, a stranger, and a stranger who has a sales goal no less, in that position. Do you really expect me to be honest with a total stranger about how something looks on you? Because the chances are really high if you are asking me, you KNOW it doesn't look good. And somewhere in the store, lurking like a spider, is my boss, who would flay me alive if she heard me say something negative that caused me to lose a sale. So if I say something along the lines of "That looks good! But let me go get you blah-blah-blah, you might like that even better!" please take the hint.
Second, if you try on several pairs of jeans or pants in what you think is your size, and none of them fit right, there's a really good chance that the problem doesn't lie with the clothing itself, but that the size you're trying on is not your actual size. Which leads me to my next point...
Why obsess about the number? No one but you knows whether the pair of jeans you are wearing has a 6, 8 or 12 on the tag! The number doesn't matter - get over it. Is it better to have a smaller number with a huge muffin top bulging over the waist band, or a larger number but the pants fit you right and ultimately look better on you? Sure - if you think the number is too large, do something about it. But don't buy the pants in the smaller size because you're convinced that you'll lose weight and be able to wear them soon. Because if you're struggling to zip them, that's going to take a pretty significant weight loss, and in the meantime wouldn't it be better to have the pants that you can actually sit down in, and which you can wear with a belt after you start losing weight? The pants that actually fit you are going to look much better on you and make you look slimmer than the smaller size that doesn't really fit. Then you'll have the satisfaction of trying on the smaller size after you've lost weight and having them actually look good on you.
And last of all - please, please, please talk nicely to yourself. You know how they say if you tell a child he or she is stupid, that they will start to believe they are stupid? It's the same way with your body image. If you constantly look in the mirror and say "I'm fat" or "I look terrible", what do you think your body is going to do? Dress to your body style. If you don't know how to do so, that is an appropriate question to ask your friendly sales person for help figuring out. Make sure you aren't wearing clothes that are too tight. LIKE what you're wearing and don't dress a certain way because you think you are supposed to, or because of your age. Who cares what other people think? If YOU like what you're wearing, you'll feel comfortable and be happier. And speak kindly to yourself! If you don't, who else will?