It sounds like you're running them too hot. For a coil brand/ohm I have never used before I always start out with my wattage as low as possible for the mod, and then increase the wattage in small increments to see if it works and I like it... Right now I have a coil rated for up to 60W that I am running at 10W with good clouds of MTL vapor and I am on day #36 and it works just as good as new. And my MTL hits are like 10 seconds at a time.
It's actually kind of blowing my mind as I typically get 2, sometimes 3 weeks out of a coil, but on this latest brand of coil I am now over 5 weeks and still going strong with no end in sight. I had read a review of the coils I am using and there was a guy burning through them in 2-3 days... similar story to you.