Does NEGATIVE definitely mean no?

iv already got a 3 yr old and would like another so we are trying. i have a normal 28/29 day cycle and bd on days 9,11,12,13,14,17,18, i am now 3 days late on period and have took 2 tests still say negative so am i definitely not pregnant? i don't have any fetility problems and i do ovulate as i already have a child and i am usually always on time any advice please?