“Nothing in Scripture suggests that sexual relations started only after the Fall.”
Genesis 3:16
I will make your pains in childbearing very severe;
with painful labor you will give birth to children.
Your desire will be for your husband
Not the beginning of sexual relations per se.
It's defensible to speculate, as I do, that both the man-woman relationship and childbirth would have been, or were intended to be, before the Fall, simply ecstatic.
Actually, those verses don’t support that sex happened after the fall.
God said that the man and woman would be one flesh, and that happens in sex.
There’s simply no reason to believe that they didn’t have it until after the fall.
All that really does is contribute to the concept that sex is wrong somehow, that it’s not pleasing to God, who created it in the first place.
And if sex is just for procreation, He could have very well had women go into heat. If He didn’t mean for husband and wife to enjoy it, He wouldn’t have given them the desire for it that far outstrips a woman’s ability to conceive, even with the increased conception that was part of the result of the fall.