Negative but late ๐Ÿ˜–๐Ÿ˜–

My last period started April 21st and ended the 27th of that month. I was supposed to start my period on Friday and itโ€™s about to be Thursday with no sign of it coming(I usually get insane lower back pain for that first day). I took a pregnancy test the day after my missed period and yesterday I had an appointment for birth control and they tested my urine and they were both negative.

I know it could be other things besides pregnancy. Iโ€™m never late for my period, I actually tend to get it a day or two early sometimes.

SO my question is, have any of you had negative tests but ended up being pregnant?? How did you find out?