If you have always had regular 28-30 day cycles, it is possible that you could be pregnant since you had intercourse during the fertile period. To confirm/exclude now, you need to go for the study of serum beta-hCG
titres as it is too early for urine pregnancy
tests. HPTs can read well only after 3-7 days of a missed period with a fresh early morning sample. A trans-vaginal sonogram a week after the missed period, is another way to definitely conclude. Hope your query has been answered. Take care.