Suggest Remedy For Pain In Throat While Uttering Some Syllables

I m a singer and teacher, both can be dangerous for your vocal health. My question is, why does my throat hurt when I say sounds like h, k, etc. It seems like when I do aspirated consonants it sometimes hurts. And especially when I do a glottal stop (I think) before such consonants. I visited a doctor twice and got a camera inserted taking pictures of my vocal folds but there were no nodules or similar. I can sing for hours or talk without problems, but it s only this sound that gives me some trouble or pain.