Hello and welcome to HCM.
Thank you for your query.
Yes, it is normal to have your period immediately after sexual intercourse, when you are expecting your period sometime soon.
Due to the contraction and relaxation of the uterus
during sexual intercourse, a stimulus is sent which initiates the events that lead to a period. This is normally seen, and should not be a cause of concern.
I hope this information helps. Do write back to me for any further clarifications.