Please clarify why c-diff happens more often after ending antibiotics vs. while still on them? tested for c-diff while on meds, neg. now done, worried

No need to worry: There's a difference between Clotridium difficile symptoms and testing. When antibioitcs suppress other bacteria, it can take several days for C diff to grow to enough to cause symptoms, which might happen even after the antibiotic is stopped. But if a stool test was negative, then you had no C diff in your intestines at all. In that case, once stopping it you are at little or no risk of symptoms.