5 days late for period, lower back pain, brown mucus & little pukish feeling on day 5, 3 negative hpt, little headaches, ...am i pregnant?

Most likely not: Reasons for missed / late period include: an anovulatory cycle in which no egg is released, marked v or ^ in weight; eating disorder; over-exercising (endurance athletics), travel, significant illnesses, oral contraceptives ; other meds, illegal drug use, breast feeding, hormone imbalances and medical problems (i.e., pcos). Can repeat home pregnancy test in several days.