Hi, and thanks for your medical question on eHealth forum!
If you had periods on 25th March, did not have unprotected sex after that, then you can wait a week or ten days. At times periods are delayed because of PCOS, anemia, hypothyroidism, stress, weight gain, weight loss or due to sickness. If you do not get your periods by then, you will have to take a pregnancy test and consult a gynecologist to rule out these causes. Hope this helps. Take care!