I'm lv9 and I've never even seen this 'Full Moon' potion.
According to the IGN game guide, there isn't a 'Full Moon' potion.
The Wikia states that the Swallow potion recipe is given to you in the Prologue.
Geralt receives this potion from Vesemir in the Prologue during the Defending Kaer Morhen quest.
So you should already have the Swallow recipe available, but you'll need to craft it using the correct ingredients.
Here's what you need:
Drowner brain (1): This ingredient can be found by killing Drowners, which are blue humanoid sea monsters that are usually be found near water. Common locations in White Orchard include the southern shoreline near the ransacked village, the swamp lands to the south of the Nilfgaardian garrison, and along the shoreline to the left of the Ford signpost.
Dwarven Spirit (1): This alcohol can usually be found in Smuggler caches and treasure chests or bought from any White Orchard merchant for 47 coins.
Celandine (5): This herb is super common and can be easily found in the environment. An easy place to find them is outside the herbalist's cottage. They can also be bought from the herbalist for 5 coins each.
Ref: Gamespot potion guide
This is what Celandine looks like.
It might also be worth updating your game, as v1.04 patch has been released.