You think? There is a question? Wouldn't that be a known issue?
You have some work to do. ;) No reason a mechanically sound bike can't run the same plug for about ever...well over a year for sure.
Start with a clean air filter, a new plug and fresh fuel.
Go to
CDave's site (click on the BOLD part..click on 'Tech Tips' and 'Carb Tuning') to find the starting point for your bike, for your bike's level of modification.
If you have been riding with the airscrew all the way in and haven't noticed a huge performance problem (three plugs in four rides is a huge performance problem I'd say) chances are pretty good that CDave's recommendations will be perfect for you. You can tweak them for altitude, the performance characteristics of your particular bike (each bike will be somewhat different) and your riding style.
There are mechanical conditions that can get you chasing your tail on jetting issues. For example, you're never going to get a bike in need of a top-end job jetted too well (read: 'correctly').
Good Luck!