Edit: With the hygiene query this was prompted in part by remembering how Napoleon wrote to Joséphine telling her:
“Je reviens en trois jours; ne te laves pas!” (I will return in three days. Don’t wash!)
which is presumably referring to cunnilingus - so was guessing that, ahem, tastes had changed, and wondered what trends there have been in this area.
There's an eighth to ninth century Old Irish penitential (a text that lets you know the penance for different sins) with explicit reference to oral sex:
Nech dogni etrath o belaib iiii anni in cet-fecht ma gnathach acnapthe vii annis.
Nech touisim a sil hi gin a banscal penneth dib línaib v annos ma gnathach vii annos.
In English these are:
Anyone who performs the fornication of the lips penance for four years if it is their first time but if it is usually their custom seven.
Anyone who spills his seed in the mouth of a woman must pay full penance for five years, if it is a usual thing, seven.*
There are few references to oral sex, particularly on women, but reading between the lines the greater concern usually if not always seems to be that the greater sin is ejaculation not inside a vagina for the purposes of procreation. This is St Thomas Aquinas' view and is the one that has had the most impact on surviving literature. Unfortunately without a more significant set of data, it's possible to know what sort of sex people were expected to be having, but less so what sort of sex they were having and how much they enjoyed it. However, if there's a rule about it, the assumption is that enough of it has happened that the Church has felt the need to take a stance on it.
You can read the penitential on JSTOR: https://www.jstor.org/stable/30007320?seq=1#page_scan_tab_contents
*also interesting on a tangent is the linguistic construction here. In modern oral sex the way we talk about it is usually that your active participant is doing and your passive partner is receiving. There are exceptions but I'm not sure this is the place for a friendly chat about face fucking. Anyway, if you look at this and assume primarily hetero partners (although pre-Christian Ireland has a lot more same sex shenanigans than you might have expected), the male is the active partner whether he performs oral sex on her or ejaculates in her mouth. The assumption is that the male is always the active partner and the female always the passive receiver. Which has nothing to do with hygiene but interests me.
Not answers about sexual activity per se, but a few past answers here on hygiene which may interest you:
/u/mikedash on the smells of a city (and its people)
/u/notepaperpen on medieval hygiene (posting the thread in full here, since there are a few queries about the main answer that request a bit more specificity)
/u/voxscholasticus on whether people in the middle ages smelled bad