I and my girlfriend had unprotected sex on the night of 8th Apr. We are not sure whether i came inside or not. Today is 14th Apr and she is worried about getting pregnant. Her period is going to start on 18th Apr. She says that her lower back has been aching for the last three days (she works out) , she didn't feel like eating today and also felt nauseated. Its been almost 6 days. Is it ok to take birth control pills? will it be effective? and for how long she should be taking the pills? or we should wait until 18th? Are these symptoms of pregnancy?