is possible only,if unprotected sexual intercourse is done with ejaculation around ovulation time in regular period. Ovulation occurs approx 14 days prior to due date.So calculate your ovulation time and high risk days (6-8 days in regular period)
Bleeding in first time sexual intercourse is quite common & it is due to rupture of hymen
.As bleeding is mild,then you need not to be worried as it is auto healed in 2-3 days. Consult with your doctor if bleeding continues beyond 3 days.
Wait for upcoming period and if it is missed,then do a home pregnancy test with urine after 1 wk.
Practice safe sex
by using safe period/Em Pill/Condom etc to avoid unwanted pregnancy & vaginal bleeding.Be well.