Is it possible for some women to never get a positive urine pregnancy test and still be pregnant?

My periods don't usually come on the same day but they mostly always come on day 23-25 of my cycle. Today is day 27 and still no signs of a period (no cramps like usual, but bloated and breasts were tender). I have never had a period after day 28. The test I took today said negative but a few years ago the doctors performed a urine test and it was a false positive (I was still a virgin then). Is it possible for me to be pregnant and not get a positive urine test? My breasts were tender a few days ago and I am nauseous.. But I'm not sure if its because I'm nervous or if its something else.