Torah not given on Sinai - Mizrachi

Mizrachi (Bamidbar 11:10) They cried amongst the families concerning the sexual relations that had been forbidden at Sinai In Sifri it states that when Moshe told them to separate from prohibited relations the Jews were distressed since some were married to a sister or the father’s sister or the sister of the mother. I don’t know why they were upset now after departing Sinai that they would cry about the separation ordered by Moshe several months before. In fact even though Moshe was told the prohibitions on Sinai possibly the Jewish people were not informed of these prohibitions until Sivan when the Mishkan was erected.