The same thing happened to me. My last period was oct 7 was suppose to start it around Nov 12. But in between that time i was having wired symptoms. My boobs hurt like crazy and the spit in my mouth would make me gagg. I tested at the beginning of nov, Negative. My period date came and went had cramps like i was getting ready to start but nothing ever came. I tested again Nov 21st and was 6 weeks pregnant. So its possible that you are pregnant love.
Go see a doctor for a blood test.
Do another pregnancy test in a couple days! I was late for mine and took a test and it was negative... Few days later checked again & it was positive. There just might not be enough of the hormone in your urine yet for the pregnancy test to come out positive if you are pregnant.