I feel so unaccomplished in life?

Although I'm only 15, I feel as if my life has no worth in it. With every single thing I do, I feel as if there is always someone better out there in the world, and that I'm always second rate. Mostly, the things that I would like to accomplish, I can't, because my family is cut under short budget. But, seeing as I know many who are more fortunate than I am, they can get every single thing they can. I find it frustrating to see anything good about myself, and it's like my life is just so....underestimated. I understand that I have nearly no self esteem in myself, since my parents always praised me, as I am an only child. I find it hard to believe that when people compliment me, that it's actually true, but in the inside, I think that they just say that to make me feel good. I feel like I would like to change so much in my life, but I just don't know what to do.