Not pregnant but missed my period

Has this happened to anyone? They missed there period but not pregnant. I'm about a week late an haven't had it all the month of July. I read about stress,diet,exercise..etc.. Can cause it being missed but I haven't really been under stress or any other things that could cause it and I'm not on BC. Anyone have this problem? I read about it an it could just have missed and by the next cycle everything should be fine. Anyone can relate?