What is the cutting surface you are using? It is mostly the cutting surface that determines how fast your blade becomes dull.
I buy my rotary blades in bulk on eBay so they cost much less per blade. IMO, this works better than using a sharpener. I used to use the sandpaper type of sharpener and it did help, but I resented the time it took -- especially if the blade had a nick in it I hadn't seen. Sharpeners cannot remove a nick in the blade.