3 Weeks Late

Hey ladies, my period is 3 weeks late (supposed to get it Aug. 11th), last week I experienced some nausea and this week I've experienced some nausea again along with some lower abdominal discomfort and lower back discomfort. I've lost my appetite too. I took a hpt earlier last week and it was negative. Could I possibly be pregnant, even though the test is showing a negative? Thanks for your feedback!