How do i get Doc to listen?

My 2 month (-5weeks) old twins have an intake of 3-4.5oz every feeding. Recently my boy has been having problems with his breast milk fortifier not sitting well with his stomach, so he throws it up. When i say throw up i mean... Throw up. Happens about 10 mins after the feed usually just as he is starting to fall asleep and splat! Everywhere, requires a change of everything from clothes to blankets and what ever he is laying/sitting in has to be cleaned.

So like any good mom would do i started trying to figure out what the cause is, I ate nothing but oatmeal for two days, no change. Lowered the temp of his milk from warm to room temp, no change. So i stop the fortifier...he stops doing it. Knowing he needs the fortifier for the calories i purchase a different brand, start slow with small amounts. He is now up to his required amount and no vomiting.

So i call up the Doc and say hey we need to change this(my insurance helps pay for it so its prescribed) he says no they need that one for the cals so limit his feed amount to no more than 2oz and burp every .5oz.

I did as Doc said on Sat. Put him back on the original fortifier, gave him only 2oz ea feed and burped...Henry was pissed!!! Not only did he have a decent amount of spit up but he screamed bloody murder for 20mins before i said screw it and gave him 2oz of just BM which he threw up. So after getting him calmed down and him falling asleep for about a hour he wakes up ready to eat so i give him 3oz w/fortifier. Hes not as pissed...calm for about 20mins after feed then throws up.

1. How can i keep doing this to him? I cant we did 3 feeds like this on Sat. Before i said enough.

2. How much does your 2mon old preemie intake?