Ah, I can totally relate.
I've changed my major erm... 3 times now? Though I think I'm pretty satisfied with my current one, but at the same time I'm always open for change...
I think the key is to really discover what makes you happy, so your career can just be an extension of it. "Sitting on my ass doing nothing forever" doesn't count, haha.
"I think that what's more important is that you should look at your work as an extension of the most natural part of you. [...] I guess it’s trying to eliminate an affectation, or an assumption, or a program, and trying to be who you are. Which is very hard to do, it takes many years actually. I tell [students] to look for the smallest, most insignificant part of themselves that gives them pleasure, and that will give them the clues into what means something." - Maira Kalman
For me, I've found out that I'm a bit of an adrenaline junkie so I'm pursuing a bachelor's in health science so I can become an emergency department physician's assistant, and I've just signed up for the local volunteer ski patrol team.
I took a while for me to come to that decision though. I was doing really shitty in school and I was also a bit depressed last semester and I basically said "fuck everything" and took a little bit a break and started seeing a psychologist so I could collect myself and find out what I really enjoy.