Late periods

My period was 6 days late, so i took a pregnancy test and it was instantly negative (the control window came though and it was still negative) My period is still late and I’m not sure what to do. I came off the pill 3-4 weeks ago, and not sure if it’s down to that But I haven’t had the withdrawal bleed after coming off! Also I have exams so not sure if it’s down to stress. Any advice Xx