they are not assumptions if there is scriptural support for the idea.
that is just it though, there is nothing in your scriptures about it one way or the other.
So one just as easily say that they were screwing like rabbits from sun up to sun down and only stopped in order to eat, poop, and sleep.
There is exactly as much "scriptural evidence" for the above as there is for your assumption...Absolutely NOTHING.
But let me ask you to consider this question, if they were having sex while they were in the garden, why wasn't she pregnant earlier?
Who says she wasn't?
Again you make assumptions based upon lack of scriptural mention.
For all you know she had ten thousand children before the fall.
Which would tend to explain who Cain and Able found to marry.
But then assuming you are correct that she did not get pregnant before the fall, there are several possible reasons.
It was not a part of Gods plan therefore he suspended her ability to conceive.
I will go with that.
And you have nothing to prove it wrong other than your
assumptions on matters with which the scriptures are silent.