No, sex wasn't invented yet.
No, just ate the forbidden fruit which upset God!
Adam and Eve were told in Genesis 1:28 "Be fruitful and become many and fill the earth". How unreasonable, unloving, and unjust would it have been for God to encourage the filling of the earth and then to prohibit the having of sex relations! However, they did not bring forth children until after they were put out of the garden of Eden. (Genesis 3:20-4:1)
The Bible showed that they did not produce children until after they had sinned and were put out of the garden. Genesis 3:6 ,23,24. When God married them they were told to be fruitful and multiply they could have relations just like married couples today. Genesis 1:28
The timing of marital intimacy between Adam & Eve is noted as happening after they were thrown out of the garden of Eden. The bible says at Gen 4:1 " Now Adam had sexual relations with his wife Eve, and she became pregnant. When she gave birth to Cain, she said: "I have produced a male child with the help of Jehovah". This NOW in the verse had application after they had thrown out of the garden of Eden.