|It is nice that you are in line for a promotion, but that could be nothing but a line from your manager. Even if you are actually in line for promotion, there are questions about the length of the line, how it is moving, and who can cut in front of you.|
The real issue is that his statement does not have much meaning. It is time for you to bring some specifics into the process, and this means more than expressing interest in being promoted.
One step is for you to make sure that your manager truly understands your qualifications and overall readiness for a more senior position. If you have had additional training or experiences that increase your suitability for a more senior level position, be sure that he is aware of them. At the same time, try to obtain a clear understanding of the steps he would like you to take in order to increase the likelihood of a promotion. You should then take those steps, and make sure that he knows you did so.
If you still find that others are being promoted while you remain in line, you should think about lining up some other options.