I am 31 and I can count the number of times I have thrown up, since as far back as I can remember, on one hand. I went through an entire pregnancy and did not throw up a single time, though there were plenty of times that I wished I would. It is a terrible feeling to be nauseous without the relief that comes after vomiting. I have tried to gag myself to throw up, like when I had morning sickness, to no avail. The few times I have actually thrown up, I have time to prepare before it happens. Like, get a hair tie to put my hair back, grab a glass of water for after, and most importantly, ensure that the area I will be spending the next few moments is spotless. I do not have the same trouble with vomit coming up and not out, but I feel your pain. It is quite a strange issue, I had no idea other people dealt with it.
I cannot imagine being able to stop yourself from vomiting. But I would get an endoscopy done to determine if there is any damage to your throat from doing this all these years. For it to reach that far and stop, is odd. I would think there would be no going back down at that point. If you are fine physically, I would seek therapy to learn how "not" to do this. I'm truly amazed that you have been able to suppress vomiting! But there is a reason, either physical (rule out first) or psychological, so see a specialist and get your throat checked out, and go from there. Take care...