I agree with Telmam that you need to keep flushing.
I discovered that I needed to flush because I had pain between my shoulder blades that was worst first thing in the morning, so there's something about that time of day.
I understand your fear of vomiting acid as I've done it myself, but only once to the point where it burned me. Probably your symptoms are not from that one time vomiting, but from the major congestion you still have that's putting pressure on your organs, meridians, etc. It seems like the flush works best when you do it exactly as recommended, so I think you should give it another go and hopefully it will be smoother this time.