No period?

Hey ladies! I'm getting kind of nervous. My period is 8 days late. I have a problem with endo, so that's probably why I haven't started. But I haven't even been cramping. And since I had my surgery my period has been close to my start date. I took two tests and they were both negative. I feel bloated and tired. And I've had a headache for three days. Any input would be greatly appreciated!