Let me be honest, even if it isn't what you want to hear: God has not promised to protect us from harm when we deliberately act foolishly or use bad judgment. And that's what you're doing by refusing to go to the doctor.
You see, your very life could be at stake - and your life is too important in God's eyes for you to ignore your health. God loves you, and Christ gave His life for you. And if you know Him, He now lives within you by His Holy Spirit. The Bible says, "Do you not know that your body is a temple of the Holy Spirit ... ? You are not your own; you were bought at a price. Therefore honor God with your body" (1 Corinthians 6:19-20).
Don't misunderstand me; it's not wrong for you to ask God to protect you. But don't stop there! Ask God also to give you the courage to get the medical advice you need - and then act on it. I am convinced that my life would have come to an end many years ago if I hadn't trusted Him to lead me to the medical help I've needed. Thankfully, He has given it to me over the years.
At the same time, don't neglect the health of your soul. Someday your body will die - but your soul will live on. Are you prepared for that day? Make sure of your salvation by confessing your sins to God and trusting Christ alone for your salvation. When we know Christ, "whether we live or die, we belong to the Lord" (Romans 14:8).