I love your question because I can see you are thinking about all the different possibilities.
Some people know exactly what they want to do from the start, but most people don't and that is totally okay!
By volunteering for veterinarians, you figured out that that specific job wasn't a good fit for you.
You are on the right track! Keep volunteering for organizations and projects that sound interesting to you.
Use all your skills - it sounds like you have some amazing interests!
Volunteering and/or internships will help you meet new people, find mentors, and guide you in your search for your perfect career. Keep a journal of what you liked and didn't like.
Talk to as many people as you can in all different fields: by talking you will describe what you like and why. Your ideas and interests will start to gel and make sense. These clues (interests) will lead you in the right direction. Watch TED talks, documentaries, and the news to find ideas.
Every time you see something that sparks your imagination, write it down. Review your notes/pictures/doodles and look for the common patterns.
Most people will have 4 - 6 jobs over the course of their lives.
Many jobs that will be important to the future haven't been created yet.
Find a field or fields that are interesting to you and become a life long learner.
Since you have two more years of college left, start with the basics: over 75% of the jobs by 2020 will require STEM (Science, Technology, Engineering, and Math)
There are many, many jobs in STEM fields and the number will only increase.
By having a solid foundation in one or more of these areas you will be prepared to take on opportunities in the future. Go to each department and visit with students and professors to see if these fields seem interesting.
One way to think about your dream job is to look at all the careers in this book (see next steps):
Do What You Are: Discover the Perfect Career for You Through the Secrets of Personality Type
Dream job: I have so many interests: I went to business school and kept asking professors about careers that combined technology with business and risk management. I kept asking the question. I kept looking for and finding interesting internships, volunteer opportunities, classes and mentors. I figured out that I really like applying technology to business problems. So for me an MBA was perfect and led to a series of dream jobs.
Check out this book and let us know what looks interesting to you.