Several infectious skin diseases also cause a rash. These can be caused by a number of infections with bacteria or viruses, and infestations of mites within the skin. Some infectious skin diseases, such as scabies, are caused by mites that bore into the skin surface causing irritation and a localised rash.
Now, as for your question about when to start taking oral contraceptives, there's really no hard-and-fast rule about when to start taking birth control pills. Starting in the first few days of your cycle is the surest way to prevent inadvertently taking pills while you are pregnant.
If you start taking Tri-Lo-Marzia and you have not used a hormonal birth control method before: There are 2 ways to start taking your birth control pills. You can either start on a Sunday (Sunday Start) or on the first day (Day 1) of your natural menstrual period (Day 1 Start).