Thanks for your query.
The discharge that you mention is normal vaginal discharge
that occurs at the time of arousal/intercourse due to vaginal lubrication
and secretion from Bartholins glands.
However, you need not worry about it, as long as it is not excessive, foul smelling, painful or with itching.
If any of these occur, you need to consult a gynecologist to rule out any pelvic infection