I agree about asking your pdoc, if doubling the dose, every other week is appropriate use. My prn states up to three times a day. I'd err to believe that implies spaced out, over a 24 time period, much like an antibiotic would be dosed, haven't had this conversation with my own PDoc. We've only discussed my concern about this meds addictive qualities.
Could perhaps, contact a pharmacist, too? A call to ask, if it's proper use, doubling a dose?