How do you boost intramuscular water retention? I get so dehydrated sometimes my brain burns and hurts.

Those sound like two very different things. Typically your cells manage this just fine on their own with just plain water intake provided the kidneys are working fine. Time to attain equilibrium is also important. For example, dumping a bag of IV fluid into someone’s veins will help replenish the volume of fluid in their blood vessels quickly at the outset. But it will move to the other parts of the body (or get dumped by the kidneys if the intravascular volume is already adequate).

I need serious electrolytes like 1 to 3 body armours to replenish followed by 48oz water. Followed by hours to recalibrate my body from nausea and migraines.

How well hydrated a person is before activity matters more for performance and recovery than we often recognize. Lots of studies of elite athletes and dehydration on performance and recovery. Also of these drinks have artificial sweeteners, that may be playing against you.

Urine can be clear but I can be so thirsty its unbearable. Literally feels like my brain is shrinking.

That sounds miserable. If better pre-activity hydration doesn’t solve the problem, you might want to speak to a care provider and make sure everything is ok with some tests.