Are you having any other peri menopause symptoms (hot flashes, sweats, etc)? It could be the beginning of peri. If there is any chance that you might be pregnant, you have to take a pregnancy test. I know that can be scary, especially if you don't want to be, but that's the first place I would start. If it comes out negative it will ease your tension, which also may be causing the delay in the start of your period. If it is negative, than you maybe just starting the peri roller coaster ride!!!!
Take care and keep us posted,