Pink Draught cures the effects of Temporary Sterility/Infertility, it does nothing to the Sterile perk if you have it.
It's possible (if completely redundant) to give yourself one of the temporary conditions with Brown Leaf or Blank Powder while Sterile and you can use a Pink Draught to remove it, but you'll still have the original perk.
...was there something confusing about 'Pink Draught... does nothing to the Sterile perk if you have it'? That item exists specifically to reverse the effects of Temporary Sterility/Infertility. If you want to treat the actual 'Sterile' perk, you need to use Evergreen's services.
The effect and the perk are one and the same. You literally cannot use Pink Draught unless you have one of the reversible conditions.