MY SISTER IN LAW HAS BEEN MARRIED TO MY BROTHER FOR FIVE YRS ALHUMDULILAH. hOWEVER SHE HAS PROBLEMS CONCEIVING AND HER PERIODS ARE ALSO IRRUGULAR. iS THERE ANY DUA OR WASIFAHS AVAILABLE WHICH MAY HELP HER TO BECOME PREGNANT????
It comes in the Noble Quraan whereby Allah states:
'To God belongs the kingdom of the heavens and the earth. He creates whatever He wills; He gives to whomever He wills, (in the way of children) females, and He gives to whomever He wills males. Or He combines them, that is to say, (or) He makes them, males and females; and He makes whomever He wills infertile, such that she is unable to conceive or cannot have a child. Surely He is Knower of what He creates, Powerful in (bringing about) whatever He wills.' (Surah As-Syuraa, verses 49 - 50)
Some of the 'Ulamaa have recommended reciting this dua in abundance and to make lots of istighfaar:
'My Lord, do not leave me without an heir and You are the best of inheritors.' (Surah Al-Anbiyaa, part of verse 89)
There's also a recommendation to recite Surah Maryam to fall pregnant. Taken from the fatwa of Mufti Ebrahim Desai and Mufti Muhammad Kadwa of askimam.org.
Since you mentioned that your sister in law has irregular periods, it would be best to consult a doctor so the doctor may advise what is best for her. She might be experiencing some medical problems which she has not been aware of all this while. Therefore, it is preferable that she sees a reliable doctor.
However, please bear in mind that it is up to Allah Ta'ala to bestow one with children. Not having children does not necessarily mean that Allah does not love that couple, rather Allah knows best when is the appropriate time for them to have children or to not have them at all. Have faith in Allah's divine decree.