PAUL'S THORN is NOT SICKNESS, it's PERSECUTION.
Here are 2 (NASB) scriptures that clarify that.
It says 'his grace is perfect in weakness, then he boast about his weakness, THEN HE TELLS YOU WHAT THOSE WEAKNESS'S ARE...Insults, distresses, persecutions...'
2 Corinthians 12:9-10 9 And He has said to me, “My grace is sufficient for you, for power is perfected in weakness.” Most gladly, therefore, I will rather boast about my weaknesses, so that the power of Christ may dwell in me. 10 Therefore I am well content with weaknesses, with insults, with distresses, with persecutions, with difficulties, for Christ’s sake; for when I am weak, then I am strong.
It's also mentioned in Numbers 33:55 (Inhabitants of the land will become a thorn in your side - NOT SICKNESS!)
55 But if you do not drive out the inhabitants of the land from before you, then it shall come about that those whom you let remain of them will become as pricks in your eyes and as thorns in your sides, and they will trouble you in the land in which you live.