Could it be true?

Hello, I'm seventeen and new to this forum/entire situation. I think I may be bulimic, or an anorexic who binges and purges(is that possible?). Last year I lost about forty pounds by eating 600 calories and running everyday. I'm a cross country runner so running was not an issue. The more weight I lost, the more obsessed I became. My lowest weight was 100 pounds, but I couldn't maintain it during the cross country season. I gained five pounds and felt great, but for some reason (god knows why) I started sneaking food and eating late at night. What started as an extra piece of bread here or a handful of nuts there, soom became an entire loaf of bread smothered in peanut butter and honey in addition to thousands and thousands of extra calories. That's when I started making myself throw up. I would eat and eat and eat and eat and then throw up. I started yo yo dieting. I would binge and purge my way to a hefty 115-120 and then practically starved myself to get back down to 105-110. I've been stuck in this cycle of binging and purging for months. Lately, my hands and throat hurt too much from throwing up, so I've started taking laxatives. Just three at first, but then three became six and six becam twleve and twelve became twenty four...needless to say I feel terrible and fat and painfully unhealthy, but for some reason I continue to eat and eat and eat. I weight 120 right now and I want to be 105. But more importantly than weighing 105, I want to be healthy. I want to have normal eating habits. I don't want to be living this lie anymore. I want my parents to be able to trust me. I want to be able to trust myself. I want to get my period again (who knew I'd ever say that!). I want to stop obsessing. I want to be in control of my life! But I don't know how. I've been in denial for so long. I don't know if I should talk to my parents about this or get a therapist or just make up my mind to change my behavior.Is that possible? Is this all in my head? Can I change my behavior on my own if I put my mind to it? I apologize for the length of this post, and for how self-indulgent it is...I'm just exhausted, bloated, and terrified. Could someone please give me some advice?