If you have had regular 28-30 day cycles all through, then you may suspect pregnancy
. There are two possibilities, either you had a chemical pregnancy, or a metropathic cycle subsequent to the stress
that you might have developed following unprotected intercourse
. You should get a blood test
done to measure serum beta-hCG levels and also get a trans-vaginal sonogram to locate the cause. You may contact your doctor for further advice. Take care.