Jesus did experience pain in His life. That was part of the point of His coming to earth in human form -- to experience what we all experience, including pain. Obviously, the most important point was so that He would pay the price for the salvation of humankind.
Mary was a human being. Blessed, to be sure, but a fallible human being nonetheless. The Bible does not tell us that Mary was infallible, and certainly does not tell us that she did not have a normal relationship with her husband.
The Bible is the only infallible Word of God.
Unfortunately, the Bible says no such thing. Martin Luther did--inventing the doctrine of "sola scriptura" from thin air. And he had zero authority to do so.
Is the Bible true?? Yes. Is all the truth of Christianity contained therein?? No. (And the Bible itself explicitly says exactly that.)