I encourage you to stop thinking about diagnostic categories. they are only marginally useful for professionals and totally confusing for nonprofessionals. Focus on the behavior and the causes of the behavior. If your child is moody and irritable and depressed, then try to enter into a dialogue with your child about that and how he or she behaves.
Go to the library and do some reading. Get on line and do some reading. There is a wealth of information out there on this subject. Each child is unique but Bi Polar does have a certain set of "characteristics". And if the child is an adolescent - it is even harder to figure out.
Good Luck