What Causes Burning Sensation And Pain In Anus While On Birth Control?

OK so, I started my period on Wednesday, as well as started using the birth control patch that day as well. Until today I have been wearing tampons. I didn t have very many left so I used a pad but also didn t have time to shower this morning. At around noon todaythe skin around my anus started hurting very bad. Almost a burning feeling. So when I got home after work I cleaned very well everywhere. After looking at my anus I seen that a brown color had started to go all around my anus. It is still hurting 8 hours later. I m not sure what to do...