I've had my period stop for a year too. Twice, actually. Both stoppages occurred when my Crohn's was really actively flaring and out of control. I lost a lot of weight and was underweight (lost 25 percent of my body weight over 6 months). I was also severely iron-deficient due to the loss of blood from internal inflammation.
My period returned the first time when I started on Remicade, which wrangled the Crohn's for a little while. My period stopped again when the Remicade started losing efficacy. Since I started Humira a year ago (and it has been an effective treatment), my period has been normal. I was in my mid-20's during those times my period stopped. To be honest, after I got over the worry that something was wrong with my reproductive system, I was a little happy to not have to deal with getting my period every month while I was suffering with active Crohn's.
Hopefully your doctor can examine you/run tests to determine what might be causing your periods to stop. It sounds like it could be anything. Good luck!