How did you decide on a major/career? How am I supposed to know what I want to do?

I've been in college for two years and changed my major once (so far). I was a medic in the Army and thought, after I got out, that being a surgical tech was what I wanted. I quickly decided against it. I don't want to deal with illnesses and death anymore. I'm currently going for a general arts degree, but I really have no idea what I want to do. I've thought about being a teacher, writer, police officer (or something else related), museum curator, appraiser, real estate agent, and numerous other careers. The only thing I knew I wanted to be is a mom, which I already am. Every time I take a new cl in college I think, "That's fascinating! How can I make a career out of it?" So far, I've come up empty handed or found out the careers I thought I'd like were vastly different than I had imagined. I love ancient history, chemistry, english (writing mostly) and so many other subjects that I don't know how to decide on anything. How did you know what you wanted to do? How many times have you changed your mind? Any advice?