Jova ... I get roughly 1 month (Atleast that is my average to date). This one I have been using is about 3 weeks old, so I would guestimate, any time now.
Weak = not even close to dead. Atleast once every day, my atty's start to limp along ... Thats the point where I pull the atomizer, dry everything off, blow all the excess crap out, dry off again, add 4-5 drops of liquid ... and fire her back up!
Have you tried blowing them out? If you haven't ... its night and day jova!