You have to do unprotected sex around ovulation time for highest possibility of pregnancy
in regular period and not the whole month.Use ovulation prediction
kit (OVP) for timing of ovulation and prepare for those days.
Actually ovulation occurs approx 14 days prior to due date of period and have to sex 3-5 days in that time.
Also you may undergo for some investigation to rule out causes of early period like stress,hormonal imbalance,thyroid disorder
,wt gain/loss etc. So consult with your gynecologist and take suggestive measures.
Avoid stress,take healthy diet with Vit-E & Folic acid
supplements,control body wt and proper sleep.