What Causes Delayed Menstruation Along With Abdominal Cramping?

My period was supposed to start 6 days ago and it hasn t. Yesterday is when I started spotting but it only lasted for a couple of hours then stopped. Then today I started spotting again it turned from brown to red only when I wipe nothing on my pad. But my areolas are darker than usual and I have been eating a lot and backache and bloating and constipation and mild cramping and really tired. And my breasts have been really tender what s going on with me?