Do you have some proper data for that?
This Reddit question has three answers with links and references. I'll copy and paste a 19th-century quote provided by the second answer. Reading and clicking the different links is very informative:
"Modesty must be an unknown virtue, decency an unimaginable thing, where, in one small chamber, with the beds lying as thickly as they can be packed, father, mother, young men, lads, grown and growing up girls --- two and sometimes three generations --- are herded promiscuously; where every operation of the toilette and of nature --- dressings, undressings, births, deaths --- is performed by each within the sight and hearing of all; where children of both sexes, to as high an age as 12 or 14, or even more, occupy the same bed; where the whole atmosphere is sensual, and human nature is degraded into something below the level of the swine. It is a hideous picture: and the picture is drawn from life." (Rev. James Fraser, in a 1867 report "on the living conditions of agricultural women and children")
You see, my society spent the time from 14th to 19th century as part of the Ottoman empire. (...) Nobody had sex in front of the kids, though! At least not in my society in the last several hundred years...
Well, Islamic societies were in many aspects ahead of European ones. It's remarkable to me that you mention the 14th century as the starting point for such records, which suggests to me they refer to the period after the Mongol conquests, which were quite thorough in destroying most of what existed before with few exceptions ("rivers running black with the ink of all the libraries destroyed" etc.), so my educated first guess, supposing your country was among the Mongol victims, is the reconstruction and moralizing that came about after that "end of the world" event saw some pretty extreme cultural changes compared to how things were done before.
What I described is common all around the world except there where it was made to change. So my default hypothesis is things weren't much different in your country before the "end times", and only came around after it, likely in answer to it ("God punished us for our sins, so we must become pure" and the like).
Maybe the Brits are particularly perverted in this sense
Nah, they were just normal. This is how humans function normally when they haven't been religiously indoctrinated into the belief sex is evil and corrupting. And even when they are finally convinced by incessant preaching that sex is evil and corrupting, cultures still change slowly, especially if people are left to their own devices. The way to accelerate that, which is what's been used most everywhere this change happened was via violence (morality policing), which does make people quickly change their behavior.