It's probably from Jean de Venette's Chronicle (section available here). He was a Carmelite in Paris, writing ca. 1360 CE. In the section linked, he talks about women "conceiving beyond measure," etc.

Overall, it's unlikely that there's any truth to it. Jean's text is a polemic about how the world had fundamentally changed after the BD. For instance, look at the section immediately after he talks about women conceiving; he mentions that these new children have different amounts of teeth, as if humanity itself has been transformed. The problem, of course, is that adults have a different number of teeth than children. So, what he's really revealing is that Carmelites and others are starting to pay attention to these sorts of things, in ways that they hadn't before. It's a turn to the natural world, to observation, that prefigures the shock of discovery the Europeans would experience 150 later.

For Western Europe the birth and marriages rates simply recovered to pre-plague levels. An observer who was accustomed to the very low birth and marriage rates during the plague years may have found this rate unusually high, but from a long term historical perspective it's the plague years that are the aberration, not this regression to the mean.

The birth rate simply recovered to the level needed to sustain a stable population as death rates were still very high, even in non-plague and non-famine years. Net population growth did not begin until the 17th c. agricultural revolution allowed for reliable large scale food production.

If you want to research this stuff look up 'demographics' - it's best to focus in on individual regions as there is a lot of variation within the general trends.