I just wanted to update....I'm 29 weeks and still sick! I'm not vomiting nearly as much, but because I lost more than 5% of my pre-pregnancy weight I was diagnosed with hyperemesis gravidum, which explains why none of the natural remedies here worked.
I'm still struggling every day, and spend most of my time in bed because the nausea becomes unbearable if I am up and about too much. DH decided this is our last one for sure.
The things that have helped me the most have been protein shakes when I can't keep any solids down, homeopathics (sepia and nux vomica), milk thistle, probiotics (tummy tune up with every meal), wild yam supplements, acupuncture, and b vitamins. Those did not cure it by any means, but sometimes take the edge off so it's not so bad.
I just want to warn the mamas looking for morning sickness relief - if you are so sick that you can't get out of bed or leave the house for weeks, or so sick that you lose more than 5% of your body weight, I think it's very important to seek a doctor's attention. An unfortunate side effect is that after months of severe illness it is very easy to become really depressed. I'm doing so much better now, but from about 12-24 weeks I was in a really bad place, physically and emotionally, and I think if I had gone to see a doctor sooner I would have been in a much better place.
I did end up with weekly or bi-weekly IVs, and in two very severe situations where I wasn't able to stop vomitting I got medication (phenergan), which helped (I did try Zofran once and it didn't help at all). So I think that for me, just twice, medicine had it's place.
Fortunately now I'm able to eat (not much, and I really hate food, but I can do it), and I'm about 8 pounds above my pre-preggo weight. Baby seems to be growing very well.