From the fuller scholia on Aristophanes, Clouds 1014, where this feminine noun occurs in the accusative case (web address 1); cf. scholion on Aristophanes, Thesmophoriazusae 254, also Etymologicum Magnum 684.55.
J. Henderson, The Maculate Muse (New Haven 1975) 109 #2 characterises a po/sqh as 'a small member or a young boy's member', adding that it 'seems to have had an affectionate and somewhat respectable tone, in contrast to the vulgar, almost violent tone of pe/os [pi 987]'.
See also pi 2115, and pi 2114 for the neuter diminutive.