What Causes Delay In Periods,fatigue And Discoloration Of Nipples?

i was supposed to start my period two days ago. i still have yet to. im tired and have fatigue all the time. i go to the bathroom a lot more my nipples are turning a darker color. and i have noticed i am using the bathroom a lot more when i go to the bathroom i feel as if it takes me alot longer than usual to make a bowel movement what could this be?