I'm surprised. The Concentree gets me through the whole day and by bedtime,(after a 5am application) it's still there but very close to my skin. Your bottle should still be fine. I can't imagine it would be bad by now. My bottle is quite a bit older than that.
I have to ask if you are using a deodorant soap? That would lessen longevity. I would also try putting it in your refrigerator and see if it "picks up" a bit.
I do use a very healthy dose but even with less, it still stays pretty well. I wish I had more insight but give the above a try and see what happens.