Ahhhh Belle. Mine was on and off for that period of time as well, but you are so young. I really feel for you.
I have no idea why mine is gone, and has been gone for quite awhile. All I can think of is that some of my stress issues (and bracing) has gone away.
I want to tell everyone though that when I cleaned up my diet of processed foods, esp. sugar, I started to feel better. At the end of the day, it's all about inflammation, and that is what you need to attack. What is causing inflammation? Well for one, a bad diet. The second thing would be alergies to food.
You wouldn't be on CZ if you weren't already aware of healthy habits. So I know I might be preaching to the choir. But I'd start researching inflammation like crazy. A really good Elimination Diet (only whole foods with no dairy or gluten) for 14 days, and then start to add them back, one at a time.
I wish I knew what my magic bullet was, but for me, I think it was major stress. Major stress causes high levels of glucose to surge through the system, as well as a host of other insidious things. Fight or Flight can last way longer than the perceived stress, and it shuts everything down, your digestive system, your urinary system, growth hormones, reproductive systems...etc etc. It's like shutting down your whole body.
The other thing is gut health. My professors in school keep saying the same thing over and over..fix the gut FIRST, then worry about everything else. Even traditional medicine is starting to understand about gut health...FINALLY.
I don't know if anything I said was helpful. I really feel for you.