Chiggers will stay on the host for a while until they are ready to feed, sometimes for 48 hours. While the mature chigger is orangish, the immature ones (what may be biting you) are blackish and barely visible to the human eye, and they're the ones that feed on humans. They will bite where clothes fit tight-like around your waist, armpits, groin, knees, etc. A bath helps to get rid of the bugs, but while feeding, they create a straw with your skin cells and their saliva. When the bug leaves, the straw remains, and that's what itches for a while. Gross.
Apparently, bedbugs can be picked up outside. They will bite and stay sucking for a while, and then the bite area becomes very itchy.