Try benedryl. Really.
I am a 6 time HG survivor. Mine was so severe though that I literally didn't leave my bed for 3 month during 4 pregnancies. I slept 22 hours a day and vomited the other 2.
A zofran pump may help as well. There is also a wrist band device that is FDA approved for HG. I am trying to remember the name but There are success stories on the helpher.org website. Some great tips there as well.