Hyperemesis Gravidarum

So there is a name for what I've got. Its Hyperemesis Gravidarum (HG). It is in the book Your Pregnancy week by week 6th Edition. Pages 88-89.
This is what is written about it:
"Nausea doesn't usually cause enough trouble to require medical attention. However, a condition called hyperemesis gravidarum (severe nausea and vomiting) causes a great deal of vomiting, which results in loss of nutrients and fluid. You have HG if you are unable to keep down 80 ounces of fluid in 24 hours, if you lose more than 2 lbs a week or 5% of you pre-pregnancy weight, or if you vomit blood or bile. Contact your doctor immediately!
Only 1 to 2% of all pregnant women experience HG. Very high levels of nausea-inducing hormones produced by the placenta may be one cause. Your sense of smell may also be more intense, which may make nausea more severe.
If symptoms are extreme, call your doctor's office as soon as possible. Even though your first prenatal appointment may not be scheduled for a while, there's no reason you should suffer. Your doctor will want to now about the problem. You may have to ask to be seen sooner than a normal first prenatal appointment so you can find some relief. If you experience severe nausea and vomiting, if you cannot eat or drink anything or if you feel so ill that you cannot carry on your daily activities, call your physician. Call if your urine is dark, you produce little urine, you feel dizzy when you stand up, your heart races or pounds, or you vomit blood or bile.
In severe cases, a pregnant woman may need to be treated in the hospital with intravenous fluids and medications. Hypnosis has also been used successfully in treating HG."

I don't know about the 80 ounces of fluids, that is quite a lot. I am lucky to get in 24 ounces of fluids per 24 hour period and I'm on ondansetron (zofran). I weighed 135 before my first pregnancy. I lost 25 lbs. That is 18.5%. That beats the 5% by quite a bit. As gross as it sounds, I have thrown up bile many, many times during pregnancy. Even while on medication. I pretty much fit right in with this condition. With Alona, I told my doctor at 5 weeks that I get extremely sick and she started meds immediately. I still lost 7 lbs and only gained 20 lbs from that point. She was shocked at the weight loss while on meds. With Natalie, we did the same thing, but I lost a little less and still only gained 20 lbs total. This time around, I tried to make it through without meds, but gave up at 8 weeks. I was already dehydrated and couldn't get up.

I also looked it up online. There was quite a bit out there about it. What I have read pretty much goes along with what I have experienced- it generally doesn't end at the beginning of the second trimester, but continues through 20 weeks and in some cases continues through the entire pregnancy. Basically they say that B6 and Unisom don't really work for HG, zofran (ondansetron) works well but is very expensive, phenergan (promethazine) works but is really and antihistamine and causes drowsiness. Zofran is a Pregnancy Class B drug (not expected to effect fetus) and Phenergan is a Pregnance Class C drug (not known if it effects fetus). The average trip to the ER to treat HG is $3300.

Here is my question:
Why does my insurance only allow 24 4mg pills of generic Zofran (ondansetron) every 25 days at a cost of $90 (I have a $15 copay, so it is $75 for them), or will allow as much Phenergan as I want?
With 4 mg of Zofran I am still feel really sick, can't do my daily activities, and throw up some of the time. With 8 mg of Zofran I feel a little sick, but can manage most of the time. With Phenergan, I don't know if it will effect my baby, and I fall asleep and am useless. I know, I've been on Phenergan plenty of times. If I run out of meds and have to go to the ER, I have to pay my $100 dollar ER copay and then 20% of the total bill (approx. $740 total) leaving the insurance to pay out $2560. This is far more expensive an option than just paying for the Zofran I need! Which would be under $1000 from week 6 to week 20 (a total of 15 weeks). So why does the stupid insurance company get to decide my treatment? Shouldn't that ultimately be up to my physician? Hmmm...