Postpartum Depression?

Does anyone know if its possible for post partum depression to start 10 weeks after giving birth? As this week has gone by I feel more and more miserable. My students are napping and I'm sitting here bawling. I have a lot of things going on but normally I can hamdle things really well. I just don't know what to do. Is it just me being down in the dumps or is it possible that it's PPD?