There are many variables that determine the life span of a reed. A well-maintained chanter reed should last for months if not years.
Two main factors will determine a reeds longevity. Moisture and air pressure. Your reed does need some moisture. Too much moisture followed by too much drying will cause the cane fibers to expand and contract which will permanently damage the reed.
Maintaining the correct air pressure is also of vital importance. Over blowing a reed is like revving your car engine at maximum. It’s going to give out quickly. Remember, the pressure at which the high A plays true is the reed’s correct pressure and all the notes of the chanter must be played and tuned at a corresponding pressure.
Is your F off?
Your F note may be sharp because the reed mouth size is too small. Use your mandrel or reed poker to open the mouth a wee bit. Conversely, if the reed is flat on F, the mouth of the reed may be too big/open.
Give the reed a gentle squeeze and re-test. If it is still flat once the mouth is a good size, then the reed is too long and will need a sliver of cane removed from the tips. This will make the reed harder to blow so the blades may need to be thinned again.