An up and down roller coaster of emotion (happy, then sad, then happy, etc.) might be more indicative of bipolar disorder, rather than just depression. But it would be impossible for anyone to tell on a message board, I think. I think it would be helpful if you could speak to a professional and get a formal diagnosis. Heck, you might find that you don't have anything at all. It can be very normal for our emotions to jump around like that. It could even be something temporary in your environment causing it.