The blade will tell you how many shaves it can give. Most are around 3. Sometimes 2 blades from the same box, one gives me 3 the other gives me 6. It is all up to the blade. You have a great shave. The next is a little off. Time for a new blade.
2-3 weeks? Mmm, that's a lot of shaves. You use it everyday? Doing 2 pass instead of 3 sure change something. Which blade are you using? I might have missed that one and should probably try it
I shave every other day. Makes me wonder if I'm missing something by not changing sooner, but the shave after two weeks doesn't seem noticeably worse than the first few shaves.
Israeli Personnas, BTW