Missing birthday entries

All my birthdays were entered into my calendar.  All of a sudden, all of the birthdays are gone off my iPhone but there is a new color coded category for birthdays.  It is incomplete and, at times, wrong.  How do I get my calendar entries back without having to retype them all?  I checked calendar.live and they were not there either.  I did not make any changes to this account.  To be honest, I was not even aware there was a category for birthdays and had been saving everything to the calendar.  Thanks.