I'm sorry to hear you and your child are dealing with a health issue. That can present a lot of challenges to the family, especially when the child's emotions about the illness come out as anger.
Ultimately, your child wants you to know and understand his or her feelings, and it's your attention that will be most powerful force in helping him or her through the feelings that have been stored up about the health issue. Bringing your attention to your child, even when you're not sure what to do, is a good move.
There's nothing 'wrong' with feeling angry over a health issue, or sad or disappointed or frustrated. Health issues can make both kids or adults feel many different ways. The important thing is just to set aside time to really listen to what it is your child is feeling, to "make room" for those feelings to just be, and to really hear them. You don't have to fix what your child is feeling, or try to change it, or explain it won't last forever. Just listen. Hear how hard it is for your child. And just let it be hard. Make yourself into a warm, supportive place for your child to just feel whatever it is they need to feel around this medical problem and still be accepted. Remember, all emotions are acceptable, even though all behavior is not. Your child may need a reminder that you can love them no matter how they are feeling, angry, happy, sad--you love them, not the emotion they happen to be showing at the moment.
Once your child has fully expressed the anger over the situation and feels heard, the grip of those feelings will loosen and your child will feel lighter, more flexible and more hopeful.
Check the resources below for examples of how this can work and some other ideas that might help with medical issues.
Let us know how things go!
Hand in Hand Parenting
This is difficult for the child and the parent. When we learned my son was chronically (autoimmune issues) ill it took some time to understand the facts, meet appropriate professionals and communicate information to the other family members, teachers and school staff regarding medications, side effects of those meds, and to find emotional support for my son and myself. Lot's of appointments with new professionals created time challenges as well. Patience, perseverience and perspective are all high on the list of what is needed. Your love and time will help your child to learn how to care for him or herself. Parent needs support as well.
Chronic health problems may affect anybody's psychological well being, but they may have a bigger toll on a child who does not have the cognitive ability to make sense of what's going on. That can breed frustration and behavioral issues.
The best approach is to consult with a pediatric psychologist. Your child's regular health care provider will be able to provide you with the contact information of someone in your area.