Hi Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern.
First of all you could have your menstrual period after having sex, in this case you would have heavy brownish or maroon coloured flow which would last for 3-7 days in total.
The other reason of light spotting could be bleeding from cervix( lower part of
uterus). In this there would be light
pinkish spotting or very little bleeding. Cervix has high blood supply & Even when cervix is healthy, vigorous sex can cause some bleeding. This mostly occurs when you have
vaginal dryness or less
vaginal lubrication.
However bleeding from cervix can be because of some abnormality in cervix. In case of cervix abnormality, even gentle sex in presence of enough vaginal lubrication could cause bleeding.
Therefore a Pink spotting could be a sign of cervix abnormality. If you have never got a
pap smear test done previously, You are advised a pap smear to rule-out a cervix problem.
Refer to a gynaecologist.
Hope this information helps