This is a place where a reference to the Traditional Ballad Index really can help, because, other than the 1997 reference by Bruce, no one is going to the source. :-) Note that Bruce is citing the first of the sources cited in the Ballad Index entry.

Any tune you have heard is modern.

I won't fully redo Bruce's transcription, but I'll give you one verse of the full-bore Middle English transcription at the end.

First, the Ballad Index entry:

Serving Maid's Holiday, The

DESCRIPTION: Middle English. "Al þis day ic han sou?t." The maid has sought this day "for ioy?e þat yit ys holyday"; she sets out even though her work is undone. She and Jack meet. Soon "my wombe began to swelle"; she dares not tell her mistress
AUTHOR: unknown
EARLIEST DATE: Before 1600 (Cambridge, Gonville & Caius College MS 383)
KEYWORDS: servant sex pregnancy MiddleEnglish
FOUND IN:
REFERENCES (9 citations):
Greene-TheEarlyEnglishCarols, #452, pp. 306-307, "All this day ic han sou[ght]" (1 text)
Brown/Robbins-IndexOfMiddleEnglishVerse, #225
DigitalIndexOfMiddleEnglishVerse #393
ADDITIONAL: Rossell Hope Robbins, Secular Lyrics of the XIVth and XVth Century, Oxford University Press, 1952, pp. 24-25, "The Serving Maid's Holiday" (1 text)
Richard Greene, editor, A Selection of English Carols, Clarendon Medieval and Tudor Series, Oxford/Clarendon Press, 1962, #95, pp. 162-263, "(Rybbe ne ree ne synne yc ne may)" (1 text)
Maxwell S. Luria & Richard Hoffman, Middle English Lyrics, a Norton Critical Edition, Norton, 1974, pp. 86-88, #88 (no title) (1 text)
Celia and Kenneth Sisam, The Oxford Book of Medieval English Verse, Oxford University Press, 1970; corrected edition 1973, #204, pp.452-453, "A Servant-girl's Holiday" (1 text)
Brian Stone, translator, Medieval English Verse, revised edition, Penguin, 1971, #58, pp. 104-105, "The Servant Girl's Holiday" (1 text, rendered in Modern English)
MANUSCRIPT: {MSCaiusCollege383}, Cambridge, Gonville & Caius College MS. 383, page 41
NOTES [320 words]: I have no particular reason to think this is traditional -- although the subject matter hints that it was preserved by the folk rather than the clergy! But a version both modernized and cleaned up was recorded by Maddy Prior and Tim Hart, so perhaps people should have references for the original song.
In addition, Richard Leighton Greene, editor, The Earliest English Carols, Oxford/Clarendon Press, 1935, p. xcv, while admitting he has no proof, thinks this one of two carols in Cambridge, Gonville & Caius College MS. 383 that, "because of their homeliness, their directness of speech, and their theme of the betrayed girl, have a strong case for consideration as authentic folk-song" -- although E. K. Chambers, English Literature at the Close of the Middle Ages, Oxford, 1945, 1947, p. 113, responds that "I see nothing in them but the work of some graceless minstrel." (Personally, I am more inclined to agree with Greene.) The other one, which also ends with a girl getting pregnant, is "Led I the Dance on a Midsummer's Day (Jack and the Dancing Maid)."
Greene thinks this is a Midsummer Day song, which makes sense since the couple lay down in the sand. ("Led I the Dance..." is certainly set on Midsummer's Day.) Greene dates the text to the fifteenth century. Sisam/Sisam, p. 596, estimates the date as c. 1475.
Despite its thoroughly secular content, the manuscript of this piece seems to have been written by a cleric, since he signs his name "Johannes." Apart from the Middle English lyrics, it contains grammatical treatises. The text is on page 41 of the manuscript.
The Index of Middle English Verse lists an even dozen poems in the manuscript, most of which (based on their descriptions in the Index) are secular but few of which look likely to have come from tradition. In addition to this and "Led I the Dance," a much less secular piece, "Saint Thomas of Canterbury," is also in the Index. - RBW
Last updated in version 6.5
File: RHRXV024

Transcription of Robbins, verse 1:

29. The Serving Maid’s Holiday
Caius Coll. Cambridge MS. 383

Wybbe ne rel ne spynne yc ne may,   [p. 41]
for ioy?e þat it ys holyday.

Al þis day ic han sou?t,
spyndul ne werue ne wond y nou?t;
To myche blisse ic am brout
a?en þis hy?e holyday.
Wybbe &c;