I had intercourse when i ovulated in january and had my period in january and february and now in march i'm 6days late?

If the last time : You had sexual intercourse was in january and you have had periods since that time - then you are not pregnant from intercourse prior to your last period. Reasons for missed/late periods: low body weight, obesity, marked weight ^ or v, over-exercise, endurance athletics, breast-feeding, ^ stress, illness, eating disorders (bulimia or anorexia), anovulatory cycle (no egg released), travel.