Don't push yourself too hard, it will only lead to worse things, such as damaged vocals and such. I suggest *being a vocalist myself* work yourself through it slowly. Don't try it all at once. I know you can do it 3nodding And to where as the gagging issue is, are you nervous or something? Stressed maybe? That usually tends to be the issue. Like myself as an example, I can't sing or do anything if I am stressed or nervous or anything. Let me know If I helped you on anything, and If you have any questions feel free to ask. 3nodding