My voice cracks in any range..mostly while starting a song

by Mayank
(Pune,Maharastra,India)

I have this problem of cracking of voice for 5/6 years and I'm fed up of this.

I am a professional singer, and while I sing my voice cracks when i have to modulate it? I have done many check ups in various and biggest ENTs... but every doctor says that there is no problem in your throat and vocal chords.

They say it may be caused due to acidity problem which i regularly has. I think cough is formed by acidity which causes this problem?

Please help me out ....I have my career ahead.
Thanks a lot
Mayank Gaur