Mazal tov on the birth of your baby!
The cramping and staining you describe sound normal. Both are fairly typical in nursing women, as the body recovers from childbirth and adapts to nursing. For the first six weeks or so after childbirth, nursing can bring on cramping as it triggers the release of the hormone oxytocin, which helps bring the uterus back to its pre-pregnancy size and position. After that, cramping may still be associated with the hormones released during nursing and their cue to the body not to menstruate. If you are still concerned, or are in severe pain (G-d forbid), do not hesitate to contact your physician.
Given that such cramps are common in nursing women unaccompanied by menstruation, they do not render you niddah or constitute a hargashah. This is especially the case when there is clear discharge, as you describe. As for the stains, whether or not they render you niddah depends on a number of factors. If they are on a colored surface or clearly smaller than a gris (roughly, the size of an Israeli shekel or American dime), then they do not render you niddah. If they may be larger than a gris and are on a white surface, they should be brought to a rabbi for evaluation. See our article on stains for further details.