The nausea part makes sense; but the burning is unusual. It could be that you are quite sensitive to the chemical. I've used Miracle-Mineral-Supplement with 1/2 cup of water successfully. I even use it to brush my teeth and swish for a few seconds before swallowing. I'm using lime to activate. It doesn't matter if it is psychological for you; or physiological. If it is repugnant, you will tend to stop using it. So, do what you can to gently coax your system to accept it. If the grape juice works, that is fine; as long as it does not have vitamin C added.
I'm definitely not one to say "go slowly"; but in this case, I think you should. Ultimately, Miracle-Mineral-Supplement will help you.