How do you find where your passion lies?

I want to do a lot of things. I enjoy doing so many things. I am almost decided that I want to do my undergraduate in psychology and go on to become a clinical psychologist. I almost know its what I will love to do. but I am not sure. truth be told, I don't know where my passion lies. I have a lot of interests but I don't know what I am passionate about. how do I know where my passion lies?