That question is a very typical one that I (and probably most people who have ever taught guitar) am very often asked. Before I go into detail to answer it I need to say that in order to completely overcome such a problem will require one to work at it for a long time. And I strongly suggest working with an excellent teacher to help you through this. He/she will save you a lot of time, effort, aggravation, etc.
(Refer to my previous article on "Choosing A Teacher".)

Most players have, at some time in their musical development, felt uncreative, uninspired or otherwise not very expressive musically. Fortunately, there are several things that can help one get over this. The problem is in being creative and expressive as a musician not as a human being, it is important to recognize the difference. We are all creative and expressive as people (that's a big part of what makes us human). One's perceived lack of creativity and expressiveness is most likely not due to a lack of creativity or expression at all, but rather a lack of fundamental musical skills. Typically the problem is caused by a combination of factors such as those in the following list: