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.
There are three different ways to start taking birth control pills. First Day of Period Start: Start your pills on the first day of your period. Continue to take one pill every day at the same time. With this method, you do not need to use a backup method as the pills are effective in preventing pregnancy right away.