Long ago people got married in Shrove and at no other time. In that way, the bride would be in her new home for the start of the year's work. Sometimes arrangements were not complete before Shrove Tuesday and then all was fixed for "Patrick's Day" or Easter but at no other time were weddings spoken of.
I never heard of any unlucky day but the month of May is considered very unlucky, so much so that if a "match" is going on, the parties try to get it fixed up so that the wedding day may be in the end of April. Otherwise it is put off till June.
It is considered very unlucky for a marriage to be put off three times. They say it will never "come off". A couple about to be married should not get photographed together before - sign they'll never be married. Neither should they present each other with anything holy - Rosary - Prayer book, etc. or with anything with a point - a pen or a brooch or a penknife or a manicure set holding a scissors. As all these points "cut love and turn it to hatred."