People have varying opinions about Paul's thorn in the flesh.
However, Paul tells us exactly what his thorn was:
"...a messenger of Satan sent to torment me."
(2 Corinthians 12:7)
So we know from Paul's own words the thorn was a messenger of Satan sent to torment him.
The question is:
Who is the messenger of Satan and how did this satanic messenger torment Paul?
The messenger of Satan may be the false apostles whom Paul referred to as servants of Satan (2 Corinthians 11:12-15).
It is possible they were seeking to destroy Paul's message and mission wherever he went.