13dpo,late af...nothing but negatives...

I barely have symptoms, mild but (not period like) cramps and pings in my lower belly along with excessive gas and full but not sore breast. Took two test today both negative. One four days ago and negative and three days before then negative. I would like to believe I'm pregnant but why am I not testing positive please has anyone tested negative several times before testing positive? My cycle is usually always the same.