Help! What is wrong with me? =(?

This morning I awoke to excruciating pains in my rectum and lower abdomen. It hurts the most when I walk around so i've been in bed for the past 3 hours. I took milk of magnesia and thought it was helping until I attempted to use the bathroom and was met with a magnified pain in my rectum and stomach. I do not believe I have hemorrhoids. In addition, I'm feeling a bit nauseous. I am 17 and a girl. I do not know what is wrong, please help!!!