I often live in my fantasy world in my mind. Am I hallucinating?

I don't think it is. Just the fact that you call it a fantasy world indicates it isn't hallucinating. That doesn't mean though it's ok to spend so much time there. Is it escaping from something? Is it a threat of failing in the real world? Is there shyness, social phobia, low self esteem or a specific fear that keeps you isolated in a fantasy world? If you're not happy & functioning well then seek professional help.
No. The definition of a hallucination is a sensory experience that is felt coming from outside but is really an internal experience. This includes hearing sounds and voices, seeing people and things, and feeling things on you. If you are aware that you are in your own imagination that is not a hallucination, nor is it any other form of psychosis. It just means you are very imaginative.