Negative pregnancy test

ive been having symptoms for abt 2 weeks. this is my first pregnancy. i decided to wait for my period to pass. I was late for 4 days and then I did 2 tests I was negative. i was very sad thought maybe something was wrong with me. Then i tried the next day again with Clear blue a digital one and it showed positive . perhaps take a few times, some times our hcg levels are too low to detect.