What would affect how long a pills effects- lasts?
A drug (medicine) I used , used to last 72 hours, now all of a sudden it lasts me only about half of that?
What changed in my body
A drug (medicine) I used , used to last 72 hours, now all of a sudden it lasts me only about half of that?
What changed in my body
?
its called tolerance.  your body is getting used to its effects and is building up a tolerance to it.   
over time, sometimes only weeks!  needing higher doses for the same effect is common. especially in pain meds!!  
your brain changes.      
either that or your condition / injury is getting worse.