I'm 8 days late normally right on time I took a test the day after I was late came up negative .?

Ok so I'm 8 days late crampy on and off for the past 8 days .I took a test the day after I was late it came up negative. Then waited a week took another one came up negative again .... I haven't had any major lifestyle changes , not stressed , and not normally late I'm normally right on with the day that I get my period any ideas...... I've also had nausea on and off during different times of the day threw up a few times also head aches that come and go for the past week or so.