Answer:
Your body is getting rid of older blood that your body did not get rid of last cycle, or that took longer than normal to get through the cervical canal.
It can be indicative of many things:
Latent low-lying bacterial infection in the reproductive tract (see fertilitysolution.com)
Low progesterone
Endometriosis
PCOS
Pregnancy
'Normal' (all things are relative, so be wary of this suggestion.)