3 day period

Hello ladies my name is val I'm 24 live in Las Vegas Nevada and I'm a mother of 3 n wife to mu husband arnie.... and I am new to this group and seeking some advice from woman .... me and my partner have been trying to get pregnant for about 11 mnths now n still nothing... every month we think we are pregnant but wen it comes to taking a pregnancy test...they are always negative. . :-( .. n it kills us ... I wonder n tell him mayb it's us or me lol...well after I had my last child my daughter 1 yr ago I strted getting 3 day periods wen bfre I was pregnant I was getting 5 to 6 day periods. .. so I'm a Lil confused on wen exactly are my fertile days or ovulation days kinda confuses me lol... well I made the story a Lil short