I always have reg periods,now i'm 4days late. i didn't have sex since my last period, so i can't be pregnant. i have bad brain fog. idk what it is.

No sex= no pregnancy: 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), stress, travel, significant illnesses, oral contraceptives & other meds, Illegal drug use, breast feeding, hormone imbalances and medical problems (i.e., PCOS). Pregnancy is #1 reason.