What Causes Delay In Periods While Sexually Active?

hi iam jasi 23 yrs old, got married in 2006 may.yet not conceived.my husband is working in abroad .after marriage iam having irregular period.whrn he comes for vacation i will miss the period but when we check for pregnancy it will be negative;this is happenning for 5 yrs.now i came abroad and living with him.i came this july.past 6 months i was having regular period.today is my 44th day of missed period .we expect that i will be pregnant.when can we take pregnancy test at home.iam nervous because whenever we check for pregnancy it will we negative.so when can i check