My period starts on the 28th of each month and usually ends on the 5th of the following month. My annual holiday starts at the same time so I want to start using Triphasil to prevent my period from happening this month. What day do I start with and in what area of the pill pack? It is the 13th today and my period ended on the 5th. What do you suggest, and will it work and is it worth it? I am 40 years old, my husband has had a vasectomy so have been off birth control for about 5 years now.