What does the grind look like before you use it? Rub some between your fingers and see if there is powder in it.
Also what happens when you run some water through the group without any coffee? Any sediment in your cup then?
It would be hard to believe that the burrs are going blunt unless youve modified it (have you?) and made them screech.
Could also be your beans - are you using the same beans you bought 2 months ago or are they fresh (ie roasted within a week of using?) As beans age they grind differently.