Hello I Am Feeling So Sick I Am Married With

Hello
I am feeling so sick
I am married with 2 years old baby.
We are using condom for birth control.
My periods due was @ 23.
I still didn't get my periods. I am having cramps, back pain and nausea. No any other symptoms like sore breasts.
I started feeling nausea today.
I went to the doctor's clinic today and got my pregnancy test negative. Doctor asked me if your periods doesn't start in a week come back.
I need to know what's wrong with me.