I'm so sorry you had to go through that! And amazed that you persisted, especially at such a young age, until you got the right answer!
I took my daughter to numerous doctors, including a top pediatric Crohn's specialist (seriously, he even wrote a book about it for parents - hah!). And HE told her to eat more fiber and suggested the problem was partly psychiatric. From the onset of her symptoms to two years later, when she landed in ER with a stricture (freshman in college), she was misdiagnosed.
Her cousin had a similar experience. She has Celiac's disease, but was misdiagnosed as depressed for 7 years!! They gave her anti-depressants. She tried to tell them, "I'm not depressed...I just don't feel well," but they wouldn't listen.