How do I pick a career if I've excelled at everything I've done, and don't really know what I want to do?

Why do just one thing at a time when you can do multiple things at once? Here is a game plan: Go to the chamber of commerce and start your own company; Code your own website and sell your paintings there; Code another website and sell your books there; Code another website and let people hire you to sing on their weddings; Code another website where you write a course to learn math or physics that you sell to people (like children who have trouble with maths); Combine anything of the above. You don't necessarily have to do everything at once, but definitely combine your skills and use it to be an independent entrepeneur.

I think you could go to a good college, in a country like in the U.S. which allows you to choose what subjects you like,physics, math, creative writing, music, etc. You could start your own business like a bed-and-breakfast/home-stay which allows you to do everything you want to -manage, cook, write brochures, etc. You could also become a graphic designer or video game programmer - it involves the talents you've mentioned -art, writing, coding, math, etc. You could become a science professor and write children's books on the subject using your art as illustrations. You could use your coding skills to start a website on the same topic or anything else you like. Just because you're good at something doesn't mean you can imagine working at it 8 hours a day.Whichever field you can imagine working in for most of your day should be your choice. You may be doing what you love but you will have to give up/reduce something else in your life. Life is full of trade-offs.

Sorry to say, you sound young.  Figure out which area you're most passionate and follow that path.  You may be in the top 2-3% but who are you comparing yourself against?  You may be there because you're playing it safe (big fish in a small pond).  Move to someplace with a bigger pond and you'll be able to grow in your area of interest. I was always the best musician I knew but I realized it was because of the musicians I was hanging out with.  Even when I started gigging with musicians who had toured nationally, I was keeping up.  However, there were other aspects of the business that I didn't enjoy that made me realize I didn't want to travel down that road.  I checked it off my list and now I can explore the next passion.