It sounds to me like your eating is disordered, but i am not sure if it would come under an Eating Disorder diagnoses. The choking fear sounds a bit like a food phobia, but its great that you are no longer scared of that.

Depression can definitely decrease appetite too.

The problem is that "I honestly don't believe I'm sickly underweight. I have a high metabolism and this is my body type. I've tried to gain weight before, I WANT to gain weight, but it just doesn't work." are all excuses that i have given to medical/psych professionals (and myself!) in the past to hide my ED. I am not saying that is what you ARE doing, but do you think it may be a possibility?