Most likely this poem is by Yi Hangbok (1556-1618). It was first credited to Kim Sakkat in Kim Rip shijip (1977), edited by Pak Yonggu.
The thing p’um character is written with three boxes; each box means mouth. The stream ch’ŏn character is written with three upright lines. The kwŏn character in line eight literally means fist, but it can also mean a stalk, a loving aspect or perhaps even lovingly.
The rhyme is in/yŏn/ch’ŏn/kwŏn; tones match and verbal parallelism is observed.
Second month; neither hot nor cold;
wife and concubine are most to be pitied.
Three heads side by side on the mandarin duck pillow;
six arms parallel beneath the jade quilt.
Mouths open in laughter—thing p’um;
bodies turn on their sides—stream ch’ŏn.
Before I finish in the east, I’m at work in the west.
I face east again and deploy the loving jade stalk.