My periods get late everytime about 45days or 60days then it startedwat can you do to get them regular?

my periods get late every time about 45days to 60days then it started,wat can i do to get them regular???secondly after how many days after period i can do sex??when i know after sex pregnancy chances???i have no baby yet i got married last year about 1 and half year ago,in the begining we have not decided to give birth but now i wish to have childrens...