According to Catholicism, what did St Paul mean by "a thorn in the flesh"? We see St Paul writing at 2 Corinthians 12:7 (RSVCE)


  And to keep me from being too elated by the abundance of revelations, a thorn was given me in the flesh, a messenger of Satan, to harass me, to keep me from being too elated.


What exactly was St. Paul referring to here ? Was he telling an idiom of his time in order to show that he was undergoing some painful medical condition ? Or, was he referring to the temptations of flesh? Are there any authentic interpretations from the side of Catholic Church on the saying of St Paul?
The Catholic Haydock Commentary on 2 Cor. 12:7 says:


  A sting of my flesh,[1] an angel, or a messenger of Satan, to buffet me. The Latin word [stimulus] signifies any thing that pricks or stings, the Greek word [σκόλοψ] a sharp stick or pale: he speaks by a metaphor, as also when he says to buffet me; that is, by causing great trouble or pain. Some understand by it a violent headache or pain, or distemper in the body. St. Augustine mentions this opinion, and does not reject it, in Psalm xcviii. tom. 4. p. 1069.; in Psalm cxxx. p. 1465. St. Jerome also speaks of it in chap. iv. ad Galatas, tom. 4. p. 274, Ed. Ben. But St. Chrysostom, by the sting, and the angel of Satan, understands that opposition which St. Paul met with from his enemies, and those of the gospel; as Satan signifies an adversary. Others understand troublesome temptations of the flesh, immodest thoughts, and representations, suggested by the devil, and permitted by Almighty God for his greater good.