To chime in, after reading all other thoughts.
Genesis 1:24-25 tells us why a man leaves momma and daddy and joins to his wife: because she is "bone of my bones and flesh of my flesh." This is the first marriage. It then tells us how marriage is recognized in God's eyes: "they shall become one flesh." When you have sex, you are joining two people together into one. 1+1 = 1. Biblical math!
I believe they had sex before the fall, whatever perfect form that looked like. I also believe that, at the fall, they realized they were naked (eyes opened, telling good from evil) and clothed themselves. Prior to that, they were naked, but didn't know nakedness to be bad or good. The fall "redefined" that. This is why many of us don't like being naked in front of our spouse, even though biblically, there's no foundation for that. We know from Gen 2:1 that they started having sex for the purpose of procreation. I believe prior to that, it had been for recreational purposes.
I DO agree with @SeekingChange that in the OT, nakedness was a form of shame and therefore viewed as a bad thing. We see this with Noah after the flood. This wasn't God's original design (which is was sin is, a break in the design), and therefore our corrupt, though redeemed, minds turn it that way.
I tend to believe that Adam and Eve had perfect intellects. They had perfect knowledge. How else could Adam's sons have learned how to craft metal and make things? It had to be passed down from Adam. He was also made with the perfect ideal for sex, as men are made in the image of man and God made sex. He also had to have been INCREDIBLY intelligent, because he named all the animals of creation. You can't do that without being smart.
Those have pointed out that we really can't know...you're right. We DO know that they weren't ashamed of being naked, they fell, then they were. If they had had sex before and after, think about the impact of THAT alone. You've been having amazing sex with "bone of my bone, flesh of my flesh", literally living naked all the time, then fall...and realize you're butt naked (pun intended). And the next time you go to have sex, it's different, because your mind is changed now. But they STILL had sex, because Cain happened.
Do we know for sure? No. But we DO know that God made sex, sex is glorious, and that, as some have said on here, orgasm can almost feel heavenly. Here's a thought for you, with no way to biblically prove it. When you have an orgasm now (male or female), it is inside a corrupted body and mind (who among us isn't distracted during sex from time to time). Imagine what the first orgasms was like for them, if they had one (which I sure hope happened) PRIOR TO THE FALL.
But by the grace of God I am what I am, and his grace toward me was not in vain. -- 1 Corinithians 15:10