Implantation or Aunt Flo???

I think the answer to that question is neither. I think that if you began to engage in three weeks post partum that the spotting could be contributed to various explanations. Possibilities include (but not limited to) recent delivery, infection, implantation, cycle, and what not. The symptoms you describe could either again indicate pregnancy or a recent delivery. If symptoms persist ask the physician at the routine 6 week examine.