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.
Birth Control Pills - Periods. When should I expect my period when using birth control pills? If a combination birth control (estrogen and progestin 21- or 28 day birth control pill pack) is started for the first time on the Sunday after your period begins, your period should occur about 25 days later. Ask your healthcare provider which day is the best to start your specific pill pack.