C.B.
I can really empathize with your situation. I am pregnant with my 4th child, and I can honestly say that the most stressful period of my life was when my 1st born threw up EVERY night for almost 2 years. We had the medical tests done, but it was more of a matter of anxiety. It is pretty simplistic to tell a parent to teach their child to not have a temper tantrum. I really like the calming technique the one mom mentioned. I can tell you from experience that no amount of negative discipline worked. (I even went to the extreme of making my daughter clean up after herself.) As I got older, I came to realize that it only made the situation worse. It is so easy to become angry, and it is easy to feel like your child is doing it on purpose. In our case, our daughter always did it for bed. It did take her a while to grow out of it, but she eventually did.
As for long term, Julia is now 11, and when she is feeling extremely anxious, she still gets sick to her stomach. She does not throw up like she used to. It took me a long time to accept her personality when it comes to stress and anxiety. I am a very confident person who thrives under stress. Julia is more like her dad, and she internalizes it. Once I was able to accept this, I was able to help her deal with situations that caused her anxiety much better.
Just know, there are other moms out there who have struggled with this. I felt very alone when I went through this, and I blamed Julia until I was able to step back and learn how to better cope with it.