Hi there Louis! Being an Astronaut is a very challenging and rewarding career choice if that is what you want to do. Fundamentally, an astronaut is a person that gets trained the by the space program to be a crew member of a spacecraft. Astronaut training doesn't start until you actually get selected in the program.
So let's look at the requirements for that. First you will need a Bachelors degree in any STEM field. This could be anything, but since it requires so much work you will perform better if you pick something you actually enjoy.
To determine this, look at what you do in your free time. Do you enjoy picking up a geology book, learning all about it and doing experiments in your backyard? (e.g. Astronaut Joseph Acaba has a B.S. in Geology) Or is it something else?
If you aren't sure, it's time to start reading about what the degree actually entails. What classes would you have to take? Can you sit through multiple classes about organic chemistry or would you prefer biology?
I went to the Georgia Institute of Technology for Mechanical engineering, so I am familiar with their site. You can browse any curriculum, here is an example for the BS ME degree program of study (open the PDF link)http://www.me.gatech.edu/undergraduate/ug-curr
Another good site for a list of all courses available http://catalog.gatech.edu/colleges/coe/mechanical-engineering/#coursestext
GaTech has a minor in Robotics, these are the classes that it entails. http://www.catalog.gatech.edu/programs/minor-robotics/#requirementstext
Lots of programming hardware. I personally had a Robotics class and it was a lot of fun.
The best way to identify what profession you may want to do is to actually start doing it. Read through some homework problems on related course topics. Do you find the real life application of it interesting? ( don't worry at all if it looks complicated )
Another way is to shadow someone who is already doing that. Could be at an internship or summer program.
NASA needs a wide range of experts in many different areas, like I point out here. https://youtu.be/RhegM6XEtcw?t=579
I started out as an Aerospace Engineer, but found that was too specific of a major. So I switched majors to Mechanical Engineering since it is more broad and I can find what I'd like to specialize in.
I discovered that the moment I took the introduction to aerospace class. If you can expose yourself early on to what you think you are interested, you can save a lot of time (and money) if you decide to switch later on. There are syllabus available for every class. Check them out.
Many Astronauts have a pilot's license, that is something you can pursue while or after doing your degree.
Lastly you'll need to be physically healthy, so don't just stick your head in the books. Go out, do exercise, and eat a healthy diet.
Hope this helps and feel free to ask more questions.