M.B.
It sounds an awful lot like celiac. Celiac is an autoimmune disease caused by an intolerance to wheat gluten. Nausea and vomiting are symptoms and the migraines are too. I used to have migraines all the time and a sensitive stomach. I have not had a migraine since I've been on a gluten-free diet (and I had debilitating migraines once a month on average).
Another thing that points to celiac is the fact that the symptoms were gone when you were pregnant. Pregnancy suppresses your immune system so that your body won't reject the fetus (a foreign entity). Since celiac is autoimmune that suppression can make the symptoms subside (puberty can do something similar due to all the hormones and it sounds like that happened for you then, as well).
Celiac is the most highly underdiagnosed genetic disorder in this country. Here's a basic overview from the NIH website:
http://www.nlm.nih.gov/medlineplus/ency/article/000233.htm
(Noting that nausea and vomiting is one of the top symptoms - both my boys had that one)
And, this one discusses Celiac and Migraines:
http://www.webmd.com/migraines-headaches/news/20030321/mi...
(both my sons had constant headaches and I had migraines)
You can get yourself tested here: www.enterolab.com
Your doc can run blood tests, but they're not as accurate.