I just asked my doctor if he would write me a script for a 60 or 90 day supply in case of emergency in addition to my regular script, and he said no problem. I filled it at Walmart, and paid cash.
Took the other script to my regular pharmacy. No problem. The insurance company dictates that script shall not be filled until you are down to your last 3 pills from the last fill date.
Sometimes, I put one pill back in a spare bottle each month too.
I remember now that it was the insurance company restricting the amount.