Clarification on pregnancy symptoms

Patient: I am 23 year old girl. My last period blood loss started on 29th Feb. After 5 days (4th March) I rubbed with my boy friend. My boy friend ejaculated in the process. I was wearing my underwear and thick jeans. My boyfriend was wearing underwear and boxers. Please let me know is there any chance of pregnancy.I found a blood spot on my underwear on 15th March. Is this the sign of pregnancy?Can I concieve after 5 days of my first day of blood loss during periods? Please help in clarifying my doubts. I am very tensed.