On the other hand, I have a friend who is a painter but he spends many weeks every year visiting zoos and wildlife parks and refuges all over the world to take hundreds, if not thousands, of photos of the animals for research for his paintings. Many, many people have tried to buy his photos and many companies that sell posters and large pictures have contacted him but he refuses to sell them because he is using them to paint. It just shows that there is a large market for good animal photos and you could spend a lot of time being greeted by the lions at a lot of zoos.
If you love writing the best advice I can give you is to write, write, write. If you can't figure out what is bringing you down possibly start a journal and write about anything that bothers you or the things that lift you up, write poems and songs, write about the soup burning because there was so much going on, whatever comes to mind write. Try setting aside time, even it is short, to write every single day. You don't have to tell anyone about your writing or let people see it before you are ready but even if you think something you write is awful KEEP IT! It may be better than you think but no matter what when you look back at it years from now you will realize how much you have learned and how far you have come and you might even learn how good you are now when you look back at it.
You sound like a writer in the making. The majority of writers are introverts like you say that you are and most writers feel things very deeply and have a melancholy type personality which at times can feel a bit like depression. Since you are still school age you are going through that period of time that drives everyone crazy; the time when we want to be independent but we also want our parents to be there to help us when we need it. Being a rainbow child (the one after a loss of a child) don't make things easier, probably, we have one of those in our family so let me tell you that though it seems a real pain at times just remember when your parents seem unreasonable it is because they feel that you are special to them and they are trying to keep the bad things away from you.
This can be a time when you feel the need to choose a path to your future but most students have too little experience with all of the paths to feel that they can make a good choice. That makes for a lot of stress. A word of advice. Don't sweat it so much because the choice of a career is not set in stone. If you change your mind you can change your career. Your friends are going through it too they can just hide it better or because they don't have a writer's type personality don't feel it quite as deeply as you do. Use those feelings to write, that is what they are good for and what makes for a good writer.
If you feel the need to do something work on getting to know yourself. It sounds dumb for someone to say that but only when you are in touch with who you are and can learn to love those parts will you stop feeling so empty. Use this time until you graduate and get old enough to go out on your own learning about careers that will fulfill you so that you can make better choices when the time comes. I can already get a sense of so many good things about you, embrace those and try to expand them. Try to break out of thinking so much about yourself and look around for someone who looks as if they need a kind word or deed; even an introvert can say hello or tell someone that their top really makes their eyes shine or their color light up, introverts can pick up items elderly or handicapped people drop or open doors for those that are struggling. When we look for ways to do one small kindness every day it is hard to get so wrapped up in what is missing with our lives, sometimes what is missing is kindness to others.
Come here and write 5 things that you are grateful for every day. It's hard to feel empty when you see how many blessings you have in your life. Sometimes it's hard but those are the days that we need it most.
Try to look for the best thing that happens to you every day. They won't all be earth shaking but I am sure that you will find something good in every day. Make sure that you try to boil it down to one sentence and write it down every night. If it turns into a story, song or poem as will sometimes happen that is fine but keep a listing of the best things that happen every day. At times when things seem hard it is good to look back over that list.
I don't expect you to take every single thing here to heart and try to do it the way I would. Far from it. I expect you to take what you need from it and leave the rest. I just hope that something I have said rings a bell in you and gets you to thinking of ways that you can take the proverbial bull by the horns and make it yours so that you can start feeling more fulfilled every day. I wish you luck as you go forward. Keep us posted, please.