Do I possibly have depression?

Ok, so I don't just mope about 24/7. For the most part, I am happy. But lately I have been having problems sleeping, and my appetite has changed [I'm hardly ever hungry anymore]. I've had bad physical pain for a while now, but lately it has been much worse. Occasionally I will have a sudden onset of sadness, for what seems like no reason. It usually happens for about 15 minutes, then goes away, but it is unbearable when it happens. It is times like these when I am sure I have depression. But my mom doesn't think I do because I'm normally not sad. Is it possible I have a form of depression, or that I'm beginning to show signs of it?