Finding the Right Dosage

I've been trying to find the right dosage and as I keep increasing the number of units it's become frustrating. I've been increasing the dosage by 5 units each time and still haven't found right number.
My question is has anyone done a second or third injection at one time to speed up the process to find the right dosage or is it always one injection and if its not enough wait until tomorrow? I'm using bi-mix not tri-mix so a second question is has anyone had success with tri-mix but not bi-mix