Now I am a Baptist, or at least becoming a Baptist: therefore I too doubt that the spiritual gifts acquired by the New Testament early Church is not present today. That being said, I do believe there is a huge flaw in the argument that states that examples of Paul using, and advising the use of medicine is somehow evidence that he himself lost the gift of healing over time. This is a powerful argument that stumps many: when I heard it while listening the Thru The Bible by John Vernon McGee, I felt dumbstruck. Though it is very convincing, after some critical thinking, I asked myself: how could a person with the gift of healing not be able to heal themselves and other believers? and after some time the answer came to me: the gifts of the Holy Spirit (speaking in tongues, interpretation of tongues, discernment of spirits, prophecy, and healing) were used to spread the Gospel; they were meant to be the signs and wonders that would cause people to believe that Jesus is Lord and they needed him as their savior. I believe that only those who are not yet saved are able to be healed by a person with the gift of healing; a person already saved cannot be miraculously healed, even by a person with the gift of healing.
I am also a Southern Baptist. I am that because from what I have spent a lifetime learning tells me that the Baptist belief's are the closest to actual Bible teachings.
In response to your question on why Paul was not able to heal himself, remember that he also did not heal Trophimus and left him sick in Miletus.
Neither did Paul heal Timothy.
Also just as true is that "Jesus did not heal everyone at the pool in Bethesda".
It may help you to understand that God did not save Saul and David because he wanted them to face the consequences of their sin. Rememeber that Paul himself said that "Among sinners, I AM CHIEF".
No One did more to harm the cause of Christ than did Saul as he in fact not only gathered believers to be executed, He was one who cast the 1st stone. Those actions have consequences EVEN THEOUGH HE WAS SAVED.
That means; if we have used drugs before becoming a Christian and the drug had damaged something in you, God may not heal you. He might leave you to face the consequences of your sin.
Let us say that you become a child of God, and while indulging into sexual immorality, you picked up a chronic disease, God may not heal you. But that will be if leaving that infirmity in you helps you to serve him better.
You see, if God healed us of our immorality and sinful acts with out repercussions, then everyone would would get saved....
.NOT FROM FAITH IN THE GOSPEL BUT TO GET SOMETHING FROM GOD.
David and Saul came to understand that God is Alpha Omega; the beginning and the end, without him there is no God and God does what He wants to do and when He wants to do it and does not have to explain His reason to us.