Hi E.,
My goodness, what you have been through! Well, I have good news and bad news for you. It could end tomorrow, or it could last throughout your entire pregnancy. That is pretty much it in a nutshell--every woman and every pregnancy is really different.
With #1, I had a perfect pregnancy (given how she was for her first 6 months, I wouldn't have had another one if it hadn't been wonderful!) With #2, God had a sense of humor. The pregnancy was difficult--not like yours, but difficult--and then she was great once she was born.
Here is what worked for me: I listened to my body. I see a dietician weekly and that is what she told me. Literally, I lived on McDonald's and clams. Specifically, a Big and Tasty meal--french fries and regular coke and all. For months that was all I could keep down--and, mind you, it wasn't like I was eating a whole lot anyway. My dietician wasn't thrilled about this, but I just couldn't tolerate the thought of anything else nor could I actually eat anything else. Bananas were the absolute worst. I did exercise every single day and made sure that I was drinking water. I ended up only gaining 15 pounds overall--not as if I couldn't stand to lose a few anyway--and lost it fairly easily/quickly after she was born.
Hope this helps some. Whatever you can do to make yourself feel better is what you should do--flat coke/ginger ale/saltine-type crackers--whatever! This is a special time for you and you should focus on yourself. Don't forget... you can always consult your OB.