I am sorry you have had such a bad time! I can totally relate to horrible headaches and the throwing up stuff...been there too many times to even count! But....there is hope!
My advice to you about IVSM as a very experienced IVSM user...yep USER...I have discovered that having it mixed with D5W instead of saline serves a few purposes...1) it cuts down on that nasty nasty taste and 2) it's much kinder on your veins and 3) much less sodium in your system which equates to less fluid retention and weight gain!!
Now mind you...I have had more 3-day IVSM infusions than I can even count at this point in time so these are tricks that have worked for me....they may not work for everyone, but they do work for me!
Helping with the stomach upset...oh yes, that would be me! Slimfast or Atkins type shakes...they taste good and are low calories. Even those new breakfast shakes or liquid yogurt. Anything that coats your stomach. Helps immensely.
I cannot tolerate gatorade but others swear by it but you need to push fluids. Anything...water, cranberry juice, anything without caffeine. Caffeine dehydrates you. Eat small meals.
As for the oral taper....you will find opinions all over the place, but personally, not me. I get no benefit from it, does more damage to my stomach than I get benefit from the taper. I don't get the "high" from the steroids so there is no need to taper me off. I sleep and am lethargic from the IVSM and oral steroids do nothing to help lengthen the effects of the IVSM...
Some people have problems sleeping so if you doc won't give you a sleeping aid by RX, get an Over the Counter sleep aid. There are plenty out there so talk to your pharmacist. I don't need it.
To get rid of the nasty taste - sucking on lemon drops or peppermint candies...Riverwild had some good suggestions as did Gazelle.
Good luck and I am glad the headache went away. Don't be surprised if you get one from the IVSM...it's normal but will go away. Also be prepared for the red face. That will go away too.

Rest rest rest...don't overdo....you may feel like Superwoman...but rest is what your body needs right now...so rest rest rest!!!!