Perception is reality. You're personal brand is not what you think it is, rather, it is the sum of other peoples perceptions of you. Do you know what your "thing" is?
If you're looking to understand how you may be perceived, but aren't a big fan of all the negative feedback that might entail, I recommend a tactic I learned from Bob Quinn, a professor at the Michigan Business School. He recommends sending an email to 20 of your close friends, coworkers, and family and asking them for your "best self" feedback. That is, what about you makes you really great.
Do this, get the information back and work to enhance your strengths (or the ones that you choose to build your brand upon). In my opinion, a much better way to go about developing your personal brand than dwelling on "fixing" perceived negatives.