I am so confused because my cycle has always been so easy! Regular, no severe PMS, if I was late I was pregnant.

This is the first time in my life my cycle is being an asshole. And I am wigged out. I am a week late, I have horrible cramps and backache, constipation, headache, insomnia. Last night I thought I was finally going to start my period! Nope just a little teaser of some brown discharge that is gone this morning. Tests are negative. I seriously am so confused.