Hi Mel, others have explained the bad news to you already- what you didn't know has cost you. I suggest you pick one of them for Best Answer, whichever one you think explained it the best.
I am just here to give you a word of encouragement. You got out on your own very young, and by doing so you have had many learning experiences: about life, about people, about personal finance, about roommates, what helps, what hurts, etc.
You have most of your life ahead of you, and none of these learning experiences will go to waste. When a more sheltered person is 30, they will just barely be beginning to figure out some of what you already know. Your early start, mistakes and all, will benefit you, because you will be wise before your body gets old, setting you up to do really well during the prime of your life, which is still far in your future.