I think i have an eating disorder. And if i do what should i do?

You need help! Yes, you do have an eating disorder - or are at least heading in that direction. It may not have be long enough yet to take its toll, but it definitely will. Anorexia kills people all the time.
You need to tell someone what you've been doing - a family member, a close friend, a counselor, a therapist...anyone trustworthy who can help. You can beat this before it's too late.

You have an eating disorder, see your doctor. 300 Calories a day is not enough.

You honestly don't sound like you have the 'anorexic mindset'. I mean, anorexia isn't really just a diet...and being obsessed with diets and exercise doesn't sound anorexic/bulimic, it sounds more of ED-nos (which is still an eating disorder, btw) Plus, your BMI is NOT underweight (it's 22.5), to be considered anorexic, you must have a bmi of 18.4 or lower.
But then again, anorexia is not a physical disease, it is a mental one. Do you feel cold all of the time? Is your hair dryer, weaker, or falling out? Are your nails yellow/gray-ish/cracking or breaking really easily? Is your skin lighter in color than compared to before? These are all physical symptoms of anorexia.
Are you obsessed with your body shape/size? Do you get 'high' (haha) or giddy off of losing weight/losing inches off of a certain body part? Are your thoughts constantly surrounded around food? These are some mental symptoms of an eating disorder. (EDnos, Ana, or Mia)

You can Google "eating disorder quiz" if you'd like.