I have been experiencing severe lower back pain for around two weeks, and right now im very nauses. i've been very tired, and moody about EVERYTHING. I'm 16 and earlier this month i has unprotected sex and let him ejaculate in me. I was scared i might be pregnant so i took a test last night and it said negative. I started my period but its dark brown and very heavy, what is going on with me?!!? Sorry if this is to much information, but i dont know what to do.