All atomizers adn cartos eventually die. usually you get sick of them because of a stiff draw or the taste goes south before the coils actually burn out. while there is the temptation to try to squeeze every bit of life out of something, this is one area where you have to just accept that this is a hobby/practice that is full of consumable and throw-away supplies, cartos among those. As you vape, virtually all juices have some component that does not vaporize. those parts of the juice like sugars and some of the flavors and almost all colorings either concentrate in the filler of the carto or they burn on the coil or "carmelize" in the fibers near the coils. as you add more juice to top off a carto you will see that the color of the filler starts to change to something murky over time. You can sometimes clean out cartos using alcohol or hot water and extend the life a bit, but i gave up on that a long time ago. it takes time, and a wet carto can start growing mold or fungus, they need to be dried out before you can use juice in them effectively again, so it ends up being a pain at best and it could even become a health hazzard.
This is one area where i tend ot dislike the pen style e-cigs. many of them have connectors that are almost unique to their brand and replacements get expensive. A cheap starter kit often leads to an expensive hobby if replacements are expensive or difficult to get. so i have recommended an eGo tank battery to just about everyone and then add Boge or Kanger cartomizers to it. Standard 510 thread cartomizers are rarely more than $2 each and they can be bought from any online vendor and most cities have smoke shops that stock a few e-cig supplies and many cities now have full-blown e-cig shops. getting hooked up with a local shop has alot of benefits in terms of support and social conncections. they often have sceduled "vape meets" where you can bring your PV and sample lots of different things without having to buy bottles you will never finish.
Keep at it, just throw away carts as they get gross and be ready to do it pretty quickly. hanging onto old carts will only make your experience less enjoyable and may even make you better toward the practice adn the culture.