My heart goes out to you, because every single parent has a hard road to travel -- and your fears that you may have a life-threatening illness only make your burden heavier.
But let me ask you a question: What do you think God wants you to do? Perhaps you haven't thought about this, or perhaps you have -- but either way, I want to assure you that God is even more concerned about your situation than you are. He knows your fears, and He also knows your struggles and feelings. He wants to help you get through this, because He loves you -- and He loves your children also.
This is why the first step I hope you'll take is to turn in faith to God, and turn your burdens -- and your life -- over to Jesus Christ. His promise is for you: "Come to me, all you who are weary and burdened, and I will give you rest" (Matthew 11:28). This doesn't mean all your problems will suddenly vanish -- but it does mean God will help you by giving you wisdom to deal with your problems. Ask Him also to lead you to a church where you'll feel welcome, and where others can help and encourage you.
Then by all means get the medical help you need -- both for your sake and the sake of your children. If it turns out you don't have cancer, you'll be relieved -- but even if you do, you'll be able to get the help you need.