One thing to try and bare in mind that what is 'attractive' is something that is almost ENTIRELY socially constructed by society.
In many parts of Africa, an attractive woman is in fact one whom has weight, and thus there are rituals in which women are fed as much as possible and pampered in preparation for marriage (I can't, sadly, remember which exact culture does this? I had a lecture on Social Anthropology at university once and saw it there); women in Feudal Japan used to blacken their teeth to attract men. There are plenty more examples of practices that people who have grown up in Western culture may see as bizarre. (although, Western culture has had dramatic shifts in the idea of 'attractive' too; just look at how we laugh at 70's hairstyle!)
Point of the matter is, there isn't really any such thing as "what is attractive"; its all subjective. Same thing with weight; the reason you dislike the way you look may have a LOT to do with the sort of society we've been brought up in.
I don't really know if this helps? but, I dunno, when I think of it that way, I kind of feel like there's no
point in conforming to such ideals, when its so subjective; I've never liked conforming to societal pressures, anyway! I wore incredibly ugly cotton trousers as a child (gloriously comfortable stuff, I tells ya), and now, as an adult, I'd quite happily wear a colander as a hat if the mood takes me! (I do in fact have evidence of me wearing a colander as a hat, if you want evidence :3)
Same thing should go with looks, in my opinion; sure, make sure you don't become clinically obese (thats more a health than social issue

), but otherwise, really, I think its far more healthy and, in some ways, far more FUN to be yourself than something that society wants you to be.