Ultimately, you should be doing what you enjoy. However, that is a complicated thing to determine. In the same sense that an illness can exhibit itself in many symptoms, passion can express itself in many different activities, and you could not necessarily follow one of those activities to its extent while still remaining relevant to your passion. So, it's important to ask why you enjoy what you do until you understand what you're passionate about, then reverse-engineer that into an activity that fits as many aspects of that passion as possible. Then, you need to find a profession that truly applies that activity since sometimes there is a big difference in perception about a career and what people really do in it... so, there are a lot of pitfalls, which is why few people find a niche that they love.
You've identified a whole 'nother level of difficulty in the sense that once you know what you want to do, you have to achieve it... and by the time someone knows what they want to do, its not uncommon that they've already taken steps in a different direction. However, understand that many people change career tracks in life, some even several times. Unless you're close to retirement, it's pretty much popular consensus that you should do what you think is the best thing to do now. It's possible to be good at something but still execute it poorly because you don't enjoy it after long enough, so unless you have better reasons to stick it out then there's not really a point in staying.
As far as how to get there, that would be pretty specific considering you haven't given us any specific details about your situation. If you can't get in on the ground floor with your past experience, then you'll probably need to go back to college. Many people in your situation take classes part-time.
