head voice problems.

I have something wired like ulcers in my tonsils area and the back of my throat, it has a sort of burning sensations after singing and I am not able to sing in my head voice. My voice turnes into a donkey sound, like a falsetto. So how should i fix it. And also tell me how did this legendary singer sung this so well at higher notes without sounding airy. Please i have a lot of hopes.

https://youtu.be/GohkaWY6VO8