You mean the Phallus Giganticus potion?Im new to the game if i already use my potion before dealing with the ogres im stuck?
You could make your own. That requires pursuing Ziva's storyline ("the Witch"), plus either pursuing Frida's storyline (a giantess) to trying to see Maghda again without a P.G., plus getting sacred water from Liandra and horse seed from Beth, to get to where you can do that. It's not that hard other than needing levels & gearing up, but takes some time.
Or you could buy them from Daiyu at The Black Dragon in Greyport (all the way to the west). They are spendy. Beware of road hazards on the way there and back...again you probably want levels & gear first.
I generally don't take sex potions until the game asks if I want to, unless I *know* I'll be wanting them that day. Even then I don't take P.G. potions until needed in the moment.