I had unprotected sex with my girlfriend 3 days before her mensuration in which I dropped sperm outside but after dropping we again had sex after that she had her periods on 11 of last month but after 8 days she had a feeling of morning nausea/ vomiting but she didn't vomit but now it has been more than a week to get started her mensuration. we had a
pregnancy test also which came -ve is there any chance of pregnancy and how to avoid pregnancy.