BMI is absurd

So being 118 and 5'7" is on the very edge of being 'underweight' according to the BMI and that is effing ridiculous. I still have huge thighs and a tummy and look no where NEAR under weight. DUMB

EDIT: So that was my tantrum while in the doctor's office earlier. I'm so so so upset about what's happening. Like I mentioned before, I mentioned to my counselor here that I was having eating 'concerns' and she really pushed me, to my dismay, to see who I thought was an ED doctor, but is actually just a regular primary care doctor. The 'ED coordinator' of the health center called me and got the gist of my eating habits and paired me with this primary care doctor. Saw her today. I guess my last weight on a health record was 132, or 134, not sure, and that was August 24th or something. So that's 15 lbs ishhhh. Anyways, the primary care doctor did a bunch of tests on me and then said she was really worried about me losing weight that quickly, that I'm probably losing muscle which deposits protein, which is bad for the organs. (I have stage 3 chronic kidney disease so that's a no-no...)

Of course I understand the concern. I can't just stop. I seriously can't, I feel like this is holding me together and it has become so important to me. So, I bluntly told her I didn't want to stop. I told her I only wanted counseling for the mental aspect of it which is why, in my moment of weakness, I mentioned eating CONCERNS in the first place. I didn't want any of this. Now I have an appointment with a psychologist next week and I have to meet with this primary care doctor once a week. I'm freaking out. I don't know how to get out of it. The ED coordinator and this doctor are incredibly caring and sweet, and worried about me, and they know my e-mail, school account, classes, etc. I can't just run. She told me this week she wants me to eat 800 calories a day and I broke down crying. She told me I need to tell my parents. She told me if I don't, she might have to.

That's not even legal WHY IS THIS HAPPENING. Like I said, my BMI is borderline underweight, which isn't even underweight, this shouldn't be a problem, I don't want this. I. Do. Not. Want. This. I just want to cry and scream. I feel helpless.

DOUBLE EDIT: If anyone cares about my actual life, today blows. I'm in the worst mood, all I wanna do is cry. I feel very chubby today, and I'm really sick with some sort of viral infection. I have to bartend tonight 9-close, so around 3 a.m. And I'm just lonely and anxious and sad. And I don't even have my weight to be happy about today because I feel huge.