What Causes Pink Vaginal Bleeding Postpartum?

I'm 31yrs old & 8 months post partum & finished breastfeeding on Sept 14th. I havn't had a menses since I became pregnant (LMP 5/4/2009) & am not currently on any type of birthcontrol. I started with a gush of tan-ish clear fluid aprox 1/2-3/4 tbps. Today the fluid is mostly clear with slight pink tint & looks like there might be some brighter pink strands of blood. I've take a few pregnancy tests here & there just to make sure & all have been negative. The last pregnancy test was at the end of August which was also Neg. What could this possibly be?