110!? Are you kidding!? That is underweight
, according to the BMI calculator here in the U.S. I'm 5'5 and in the 115-119 range, I look sick and people aren't shy about telling me so. I'm just now up to 119 and still
As for the OP-I'm not sure where you fall on the frame scale and I've no experience with eating disorders (so I tread lightly here). But I can relate to having a physically taxing job. My recommendation would be to try to get as much
protein into your diet as possible. This is actually harder done than said, but I find protein shakes really help. When I worked as a therapist at a massage school, it was incredibly taxing; I would often eat eggs and whole grain toast with butter in the mornings, a protein shake mid-morning, and usually a big salad with chicken at lunch (and sometimes an additional protein shake after that). With dinner, again, I made sure to include more protein. It was impossible to put on weight at the pace and intensity I was working, but it kept my energy levels up and helped to preserve muscle mass.
If it at possible, I would try to gain-as you pointed out, we have a pretty wide range for what's considered healthy for our height. You stated that you feel better when you are at a higher weight-that alone should be motivation enough. But coupled with your taxing job and tendency to drop weight-that's all the more reason to try gain, if possible.
You might also consider supplementing B vitamins (especially B12) to keep your energy levels up as well.
EDIT: And...I see that you are either Vegan or Vegetarian...which makes B12 and protein all the more crucial. I don't know if you eat eggs or consume milk products, but if not, there are in fact pea-based protein powders. Might be worth trying...