Cartridges will last several years, 3 to 5 is the number I see most often, for the most part as long as there are no holes in the filter media you are fine you can even loose a band without much impact 2 might be pushing it. If you get a hole or start to notice the dirt is not evenly distributing over the filtering surface might be time to replace. If they start to get a bit dingy you can clean them with a TSP soak and dilute MA soak do a search for it you will find several results there are a few YouTube videos too.
If you are having to clean weekly your filter may be on the small side but as long as the chore is not bothering you, you can continue as your have been.