19 days late...

someone help me on advise.... AF is 19 days past due... I had a 4 day period in feb. and nothing in march but every test I take is negative...has this happened or is happening to anyone on here??? I got to the obgyn on friday but this will be the 2nd time...havent done a beta test yet might do that Friday or a vaginal ultrasound...could I be pregnant or is it something else? BTW, always had a normal 28 day cycle this is the first time this has ever happened to me. Been nauseas(no sickness) fuller breast,sneezing,headaches more often then normal,bloated, exstreamlly tired all the time, and moody. I did spot for almost a week on and off very lightly 11 days before I was sapos to start in march, it is now April 9th. Someone help me ease my curious mind.