I was in a similar pity bag, quite recently actually. Last friday I posted on here about feelings of inadequacy and low self worth, because i was comparing myself to my sister. I understand that things look great in that picture, everyone laughing and all, but I have to tell you, sibling relationships are tough. It was very hard for me to grow up with my sister. I love her very much, don't get me wrong, she didn't abuse me or anything and we have a pretty good relationship now, but she was the overachiever when we were younger. It was very hard to live in her shadow growing up, I always wanted to be smarter, faster, more popular at school, prettier, and especially more recognized by my folks. But I just couldn't compete. I see know that we were meant for different things, but I still get those days of comparing myself to her and being miserable.
My SR friends rallied and did an amazing job of reminding me that I am okay the way I am, and I am the way I am for a reason. They reminded me how dangerous it is to base my happiness and self worth on what i think other's have or don't have. And it turned out, I was envious of things that I didn't even want. We got dealt the hand we got for a reason, and the sooner we accept that, the sooner God will show us what we are supposed to be doing with it. But at the same time, it is okay to recognize what you wish you had, accept the fact that you don't have it and grieve for it, just don't stay stuck in the grief.
Most important was the gratitude list. Try to think of One thing before you go to bed each night. I've been posting on here, in the Bedtime Gratitude thread, and I always have at least two or three things now. Sometimes I also post in the Morning Gratitude thread as well. It really helps to start and end your day that way.
I hope you feel better soon!