Underweight, headaches, tiredness, loss of appetite, etc

I am a 16 year old female, 4'11ft and weigh about 87 lbs. my mom has been worried about my weight for some time. A few months ago I was about 98 lbs which my mom considers healthy and I'm not sure how I've lost 10 lbs, as I have never eaten much food anyways. Lately I have been having constant headaches, I'm always tired no matter what, sometimes when I'm just laying around I feel like I am struggling to breathe, and I almost never feel hunger and when I do eat I feel sick. I've been having stomach problems since I was a baby and have been a vegetarian diet for 3 years and also been eating less dairy for 4 years. I'm not sure what could possibly be causing this and it's hard to talk to my parents because they automatically accuse me of being anorexic, which I am not and never have been; I've always been small and never have felt insecure about my body. It's not tht I don't want to eat, I just don't get hungry. I was diagnosed with hypercalcemia a few years back but am not sure if this could be the cause, or something else anxiety related. I am a very shy person and I have always liked to keep to myself because I do have a hard time interacting with others, I also do not like eating out and I feel sick everytime I do. I've had to deal with this for too long and I haven't felt comfortable enough to go to anyone. It would be so much help if anyone had any idea what may be causing all these symptoms. I apologize if my thoughts are out of order, I tried to get in as much as I could with it still making some kind of sense.