It could be that your doctor wants to make sure that this is a more fixed problem rather than a transient one and so give you more time to think about it and time to examine your symptoms.

If, when you go back, you have the same symptoms, maybe the doctor will reexamine your complaints.

Since you are seventeen, your doctor may be hesitant to consider bipolar as of yet. Generally, it isn't supposed to be diagnosed in those under the age of 18, I believe. [Though it is done]

There are other things that can contribute to symptoms which seem like bipolar.

My suggestion is to keep a mood chart and mood journal. That way you will have something to bring back to the doctor.

You could try moodtracker.com? they have charts you cna print out and option to journal