4 lbs in 4 days???? Poss. Triggering

Okay, my therapist is being less than sympathetic, so I don't really know who to turn to.  I'm recovering from anorexia nervosa (from bmi 14.7 91 lbs at 5'6), and a few days ago I was 112 lbs.  I'm 5'7 now by the way.  The goal weight set for me is at 118 lbs, at a 18.5 BMI. So the thing is, I weighed myself today and the same scale that I've been using read 116 lbs. I'm practically on the verge of relapse right now, I could really use some support. I haven't been this high a weight in years and I'm scared as hell and confused.  I've barely reached 2000 calories the past few days, let alone the recommended 3000 for teens-I'm 16 years old.  How did I gain so fast? What did I do wrong???

Other possible reasons for weight gain: CC has been telling me for the past couple of days that my sodium intake is like, twice what it should be, I've been doing a bunch of lunges and crunches, so maybe I gained muscle, or maybe it's just water weight? I don't drink a lot though- a few cups a day, so I don't know if that would really be it. 

Replies would be greatly appreciated. Thanks, everybody.

EDIT: And I haven't even reached 600 calories today.  After lunch, I was just too depressed and lost my appetite. 

When I first increased my calories, I thought that I'd gained from 106 to 118 in a matter of around 3 days. I'd only been eating around 1700 calories a day. I stayed strong and believed my family, who told me that I DID NOT look bigger.

A week later, I discovered that I'd actually lost 3 lbs.

It's water weight! You shouldn't see real weight gain for weeks or months.

Yep, water weight :) If you haven't been eating much in the past few days it could be that waste isn't moving through your system as quickly as normal either, and some of that is sitting around in your gut.

First of all 4 pounds is not a lot even in one day. I know it is scary but even healthy people vary by that much. In recovery some people can gain double digits within a few days and why it is important to be monitored. Also your goal weight is not healthy for most people and would be considered anorexic.

I understand the fears and battle. Right now you need to stay off the scale and focus on increasing your calories to 3000 if you want to recover. Will it be hard? Yes but is the only way. Try to take one day at a time and focus on the goals. The goal is to get a healthy body, repair your organs/tissues/metabolism and fully recover.

'I'm 5'7 now by the way.  The goal weight set for me is at 118 lbs, at a 18.5 BMI.'

Abbi333, please could you explain why this goal weight is : 'not healthy for most people and would be considered anorexic.'

A weight corresponding with a diagnosis of anorexia is under 17.5, not 18.5 surely? - Just curious, as my team always told me my target was 117 (at 5' 7"), though they did make it clear that that is a MINIMUM, and following advice here, i may well overshoot this by several pounds.

Actually 18.5 is considered underweight. Also I think you know that for most of the world a bmi of less then 20 is not healthy. For recovery especially one needs to reach a bmi of 20 plus so their brain and body can heal and also one is less likely for relapse. I had in my recovery doctors set low target weights because I had been so bad that they settled for better which all it did was keep me trapped in the ed and constant relapse. When I fully recovered I got to a healthy set point and knew it had to be at least 20 bmi.