vadnad,
Could it be that some important person (such as a baseball star from Dominican Republic) will bring more guests to the oath ceremony, so that they have to de-schedule some people?
Or could it be that part of the building where the oath takes place is under construction due to unexpected damage, so that they won't be able to accommodate the group originally scheduled for?
It may take a while before you get another oath letter. Maybe you could schedule an appointment via InfoPass to speak to an immigration officer to share your concern and they'll forward your request?