My daughter’s health and how if will affect her future

My daughter has had health issues since she was eight. She is now 16. We have been to every doctor I can think of and they can not find the problem. Now we are starting over going back to the same doctors. I feel like we are just doing things to say we are trying but I don’t think any of this is going to help. She has constant migraines, is nauseous, is dizzy and this has affected every area of her life. She has missed so much school (She is home today). I worry that she will never figure this out and not be able to live a full life. She is frustrated and tired. I want to help her, but I’m feel like I’m running out of ideas and time (she will not graduate if she keeps missing school.)