Sounds like just plain not enough nutrition and your metabolism has ground to a halt.

I have never been in your situation wanting to be vegan - but have you seen Joel Furhman's eating plan? He advises people to remember you can get protein from leafy greens. That saves you from having to rely on too much soy, beans, or grains, or to have animal products that you don't want.

40 g of protein looks low even if you are very short. How are you figuring that protein amount?

I also think the fat is so low that maybe you are not getting enough to run the metabolism at all - some is needed for the machinery - hormones and what not. Or you might have the kind of body that doesn't make essential fatty acids very well from plant sources.