I think this may really depend on the person, but to generalise, I believe that lucid dreaming starts off stockily and gradually becomes more consistent. With practice and patience it's a goal you're sure to be able to accomplish. Even if it seems to be on and off now, I'm sure that will change. If it dosen't, I'm sure there are many willing to give you tips.

My adoptee, Jalexxi, had a problem where he could only maintain lucid dreams for a few seconds. The problem in his case was that he was concentrating too much. Maybe this is so with you. Show passive intrigue with your dreams and also with your HI.

Once you get the feeling for it, it's something that will most likely stay with you. You just need to feel around and get into the right setting.

Good luck!