The first thing that popped out to me in your post was the mention of stabbing yourself in the face with a ballpoint pen. That is more imminent of a concern than anything else. Safety must come first. If you aren't safe, then it's difficult to begin to sort through all those other issues. As someone with an extensive history of self-harm, I know how hard it is to stop, and that it isn't as simple as willpower. I know that, when everything feels uncertain and out of one's control, that hurting oneself can be comforting; it's the old friend that will never leave you and that will always be there for you to fall back on. It can feel terrifying to let that go. What else will you use? What if X happens? What if nothing else works? It's uncertain. I get that. As someone who has been done that road and come back, however, I can attest that it is possible to address, and that it's important not to put it off. But you need to be ready to take that leap. Are you receiving help for the self-harm? Do you have a counselor who can support you as you start working towards a place where you can consider letting go of the self-harm and using other coping skills when that urge strikes? If not, please find one. I have found DBT to be the most helpful.
I'm guessing all of this feels secondary to the fear of dying, though, huh? That's to be expected. You've already been to your physician, and he has told you that there is nothing to be concerned about. Physicians go through seven to twelve years of medical training, and much of that was in academic hospitals where they saw every type of patient you can imagine. On top of that, they likely have years of experience treating patients independently. They have seen people with the same symptoms as you before. They have seen what happened to those patients. If they're telling you there is nothing to be concerned about, it means all those patients turned out to be okay. Remember that there's only so many ways the body can be sick: yours isn't going to find a different way to do it than all those other patients did. Your tests say, in this moment, you're healthy. That's all the doctors can give you. They can't make all that fear go away. They're not trained to do it. And karma? Look at you. You are a loving, devoted mother who is worried about not being able to be there for her kids, and who has people who love her. If there was karma, you're not going to be who it strikes. It would strike the people who go out and intentionally hurt other people, and who only care for themselves. Given that it seems those people often get a clear path, I don't think karma's going to come for anyone anytime soon. You were scared and hurting when you told people you were sick. That's understandable. Try to have compassion for yourself, even though you may not feel that you deserve it.
That's the best thing you can do for yourself. I know that my self-hatred can run so deep that I often believe that I deserve so many bad things, nevermind anything good. I can convince myself that I'm the one person in the universe that doesn't deserve compassion. I've learned that, even though I feel that way, I can't act on it. Instead, I have to act like I deserve to be cared for. Do you need to cry? Then go somewhere safe, either that be a room or a person or an old memory, and cry. But keep the sharps away. Do you need to vent? Then do it. Do you need to feel sad, angry, scared? Then allow yourself to. Do you feel like hurting yourself? Why not try rubbing the spot you want to harm with a scented body lotion instead? How would you treat anyone else in your situation? I know it's hard, but try to force yourself to treat yourself that way. Even if it's only one thing a day. One good thing for yourself a day. Or even a week. It's a long process, and it's okay to take baby steps and steps backward, as long as you keep making steps.
And don't do it alone. Get help. Therapy and medication can both be good, life-saving things. Five years straight of believing that you have cancer? Jesus. Imagine what that's done to you and your body. You have spent five years believing that your life is in constant danger. There's a certain amount of PTSD that comes along with that. Counseling can help you find ways to process all that fear and it can teach you ways to respond to what you're experiencing that don't involve feeling like you're going to die. It's a long process, and I'm far from being at the end of it myself, but the goal is to have a doctor tell you that you have nodules that aren't anything to be concerned about, and accept it. You may still feel fear, but you can say, "I feel scared, and it's okay to feel that way, but I can do X instead of obsessing over it." From the sounds of it, it seems like your anxiety and hurt goes beyond health anxiety. It's the same with me. I have more diagnoses than can fit on a page! And a life history to match. Counseling can address that to. And, if your doc thinks they're a good idea, meds can help regulate your brain so that it's open to that therapy.
I'm sorry for this being so long. I hope I haven't overwhelmed you with a wall of text. If nothing else, know that you're not alone. Here, you are safe as you are. You're in Hell, but you're not the only one. We're all here with you.