How often a lack of faith is due to ignorance! If you feel like you just don't have much faith for God to heal you, it's simply because you don't have a sufficient background of faith and knowledge of God's Word!
But the provision is there for you! God has made lots of promises for our healing throughout the entire Bible, God's personal Word to each of us. "There are given unto us exceeding great and precious promises: That by these ye might be partakers of the Divine Nature." (2Pet.1:4) These are promises which we can claim and expect Him to fulfil! This is also where your faith will come from. "Faith comes"--it grows--"by hearing the Word of God." (Rom.10:17) Read it prayerfully and His Word will give you faith!
You can't say, "I'm trusting the doctor, but I won't take his pills. I'm under physician's care, but I don't like to follow his prescriptions." You have to follow through and obey in whatever you're putting your faith in.--And if it is the Lord, you're going to take the Scriptural pills and follow the treatment He prescribes: You will quote and claim His promises and stand on the Word!