Hi, and thanks for your medical question on eHealth forum!
If the semen was not ejaculated inside the vagina but at the mouth, then there is a possibility that active sperms have travelled up. If this coincided with your ovulation date then you can become pregnant. However, since it trickled down from the abdomen, many sperms would be lost in contact with air and skin, and chances are very less, but still there.
Hence, though there aren't high chances of pregnancy, you should be vigilant. Your periods may delay by a day or more due to stress. However, do take a pregnancy test if they delay by more than 4-5 days. Please consult your gynecologist regarding this. Hope this helps. Take care!