The period when you had the intercourse is safe assuming that you have regular 28-30 day cycles. This delay in the period can be caused by stress
along with several other causes like transient hormone disturbances, infections of the genito-urinary tract
, general infections, certain medications and so on. Your symptoms could be premenstrual. You can get a home pregnancy
test to rule out pregnancy, 3-7 days after the missed period. A test soon after a missed period may not read well. You can also get a blood test
for pregnancy to be more conclusive. Hope this helps.