The thorn in the flesh was apparently a physical infirmity.
2 Cor 12:7-10
And lest I should be exalted above measure by the abundance of the revelations, a thorn in the flesh was given to me, a messenger of Satan to buffet me, lest I be exalted above measure. 8 Concerning this thing I pleaded with the Lord three times that it might depart from me. 9 And He said to me, "My grace is sufficient for you, for My strength is made perfect in weakness." Therefore most gladly I will rather boast in my infirmities, that the power of Christ may rest upon me. 10 Therefore I take pleasure in infirmities, in reproaches, in needs, in persecutions, in distresses, for Christ's sake. For when I am weak, then I am strong.
Gal 4:13-16He was blinded by the light on the road to Damascus. His sight was restored when Ananias spoke to him (Acts 9:17-18), but it is possible that he continued to have problems with his eyes, even though he was not blind any more.
13 You know that because of physical infirmity I preached the gospel to you at the first. 14 And my trial which was in my flesh you did not despise or reject, but you received me as an angel of God, even as Christ Jesus. 15 What then was the blessing you enjoyed? For I bear you witness that, if possible, you would have plucked out your own eyes and given them to me. 16 Have I therefore become your enemy because I tell you the truth?