Symptoms way before getting a positive???

Has anyone ever had majority of the symptoms proving that they could be pregnant but constantly got negative tests??? If so, did you eventually get your positive after waiting it out? I've read that many women are different. Some women can get an early detection of pregnancy soon after missing AF. But others could could go up until 5 months and still won't get a positive. I think that is so strange. A friend off mind didn't get a positive until she was 6 months.