Graduation

Today I celebrated my sibling's graduations. As the oldest of five, I am the only one who doesn't have their Bachelor's Degree - or any college degree for that matter. I feel oddly about this.
Growing up, I was the nerd in the family. I graduated high school with honors, took some of the most advanced classes in Science, English, and Math, and even received an academic scholarship. I started college, but half-way through the first semester, I moved across the country. This move cost me my scholarship, strained my relationship with my family, and allowed me to eventually meet my husband.
I've thought about going back to school, getting a degree in something, but I can't figure out what. What in the world would help me with my dream of being a successful writer? Also, what defines a successful writer? That would depend on whom you ask, I think. Most people would consider me highly successful. In three years, I've written nine books, been in three anthologies, and have been asked to mentor others. While I'm beyond thrilled, amazed, and quite frankly, shocked daily by this, I still don't feel like a success. I still work and struggle with the daily grind. I'm not where I pictured myself to be, nor where I want to be in life.
But would a degree change any of that? I don't think so. I guess I could take a few marketing classes, or perhaps something for photoshop, or even some creative writing classes to hone my skills. But I'm not sure I want to do any of that.
I'm very proud of my siblings. They have all worked hard to achieve their goals, and while only one is actually using her degree, they all have that achievement to be proud of. I just can't seem to escape that nagging, internal feeling of being less, of being a failure.
The really stupid thing is (not that this whole thing isn't silly), I absolutely don't feel that a degree is that big of a deal. Many people who get them, don't even use them. There are many people with degrees that aren't working in the field their education was achieved in, and if they are, they're looking for something else, or going back to school for something else. I also know of many people who are successful without a degree.
So, knowing that I don't want to go back to school, knowing that it (probably) won't help me with what I want to achieve in life, why do I feel so inadequate?