I'm bulimic, and I don't know what to do?

Since 8th grade, I've struggled with weight loss. I've never been "fat" but I've never been satisfied with my body either. Last year I was a size 6 and I started exercising daily and eating extremely healthy, but I didn't lose anything for a long time. 2 months ago I was down to a size 4, but I was still unsatisfied with myself so I started throwing up everything I ate, only keeping down maybe a small salad. It's been like this for 2 months and my dad's caught on. Yesterday I threw up and some of the discharge was left in the toilet, and my dad saw it and started questioning me about it. At this point, I can't stop. I don't even have to force myself anymore, it just comes out. What can I do? I feel ashamed of myself for doing this. But no matter how hard I try, I can't keep anything down anymore. I might also add, that I'm 16... but I don't know if that matters.