TTC and pregnancy advice

Hi ladies I was just wondering how many weeks pregnant you was when you got a posative pregnancy test my friend said she kept getting nagative test until she was 10 weeks pregant is this possible? Reason I am asking as I am now 3 weeks late but got negative test results 2 weeks ago just before my period was due I had a small amount of brownish red spotting and I have had little amounts of cramping but these are not as painful as they are before I get my period and my breaths do feel tender.