Hi, I know exactly what you are going through.  I have three children and with everyone of my pregnancies, my siliva became so thick and If I would swallow it, it would make my stomach hurt worse and make the vomitting that I was already having even worse.   Like you, I asked my doctors about it and one said acid reflux,  the other said it was just a symptom of my pregnancy.  They were not concerned that it could be serious.  But for me it was.  I had to carry and spit bucket every I went.  I would wake up out of my sleep because my spit would build of so much that I would almost choke on it. My grandmother said that she went through the same think with her two children, but my mom didn't go through this at all with any of her three pregnancies. So I really don't know it anybody knows what the cause of this problem is but what I can tell you is that on the day that I had my kids, it went away immediately.  And from now on I know that I am pregnant before my menstrual cycle tells me a because when I can't swallow my own spit, I'm pregant.