Late and confused!

Help! I am new here and this is the first month my husband and I are TTC. I have a very regular cycle that has been 24 days the last four months in a row. This month I am now three days late, Im having sore breasts and a wierd cramping in my abdomen. However I took a HPT this morning and it was BFN. I am hoping Im not imagining my symptoms but I am always regular and wondering what would throw me off if I am not pregnant? Help! Anyone had a negative test turn into a positive a few days later?