Firstly, welcome to PC!

and secondly, I agree that now would be the time to talk to someone about what you are going through. A BMI of 16.6 is very much underweight. I've read that a BMI of 16 is "clear anorexia".

You don't need to say how much you are restricting, but I just want to point out that 1200-1300 calories is generally considered the "dividing line" where below that is considered starvation.

If this is affecting your life to the point where you can't think of anything else, it is definitely time to let someone know about what you are feeling.

good luck and take care,
lil