I am 100% sure of the date, and my period is a week late. I've had sex recently and we use condoms every time, but I heard there is a possibility they don't work if you use them wrong or something. So last night I took a pregnancy test and it came out negative. But I didn't have to pee very bad so it might not be 100% accurate. Is there any reasonable explanation for my period cycle changing?? My friend told me that it could be I'm eating differently, but make it change by a whole week??? I'm just really worried because I'm only 16 and this cannot happen to me. Anything helps 😭😭