Short answer? Go see a Psychologist. I know a lot of people are naturally averse to this (I was, at one point) but I've realised that a good psychologist is really just a good hacker - someone who's read a lot on the subject at hand (personality and the psyche), is motivated to help you, enjoys it, and has found a way to make money doing so.

In one hour with a good psychologist, they will generally be able to give you very good guidance on what you are feeling. It's not magic, it's just the power of having an informed, objective observer in a situation that encourages you to be open.

Otherwise, ask the people closest to you - your spouse, GF/BF, etc.