I'm like you in the regard that even if my bf says I've lost weight or I look good, to a point I don't believe it, and feel like they're just saying it to make me feel better about myself.
The way I see it, it's not worth starving yourself so you can be what Hollywood classes as "sexy". Look at what happens to a large portion of people in and around Hollywood: drug addicts, alcoholics, bulemics, anorexics, cosmetic surgery addicts, Hollywood puts too much pressure on people to have a specific look/appeal. They are conformists, plain and simple, and what's worse, they feel the need to be that way to "fit in".
The best thing you can do, like most of the others have said, is compare apples to apples, compare yourself, to yourself. Because like abear said, you are your own competition.
And with regards to your breasts, they're not that important. They're not going to make or break a relationship. Not to mention, 3 of my good friends have large breasts: D cup, E cup & G/H cup(and I didn't know they went up that big either!!!), and they all hate them, they would do anything to get rid of their large bust.
Isn't it funny how we're all never happy with what we have?
Lets hope all that made sense!!! ha-ha.