Cartomizers are disposable. I get some pretty good mileage out of mine. I usually get 10ml out of them before I boil them out (unless I'm using them for a tank system) or have to throw them away. It depends on the juice. Some of the lighter juices I like I can get more mileage out of the carto--one of the very dark coffee vapes I like though will kill a carto after 5ml.
I would say to try to rule out the bad carto possibility by using a fresh carto and seeing if that solves the problem. If it doesn't it could be several other factors.
The first of which is vaper's tongue. The cure to that is time, and hydration. That said you can lessen the unpleasantness of vaper's tongue by a few tricks I've used successfully.
1. Using a baking soda and water mouth rinse. I use 1 teaspoon of baking soda to 4 fl. oz. of tap water. Just like if you were going to use the same thing for an antacid. Except here you garggle with it, and use it like you would a mouth wash. Others have recomended biotene (but I have never used so I'm not exactly recommending it--just saying it is an option I heard has worked for some people here).
2. Switch up your tooth paste. I found that changing tooth pastes helped me. I don't know if it is something that would work for everyone, but it helped me.
3. Drink lots of water. The amount is different for everyone but I found that in order to not get vaper's tongue I need to regularly drink at least 2 liters of water a day, though I often drink 3-5 liters a day. If you don't like the taste of water you can use a crystal light type flavoring. I found that lemonade and fruit punch ones were acidic enough to cut through some of the PG and/or VG that may be coating your tongue. Myself I actually use a strawberry energy from crystal light in my afternoon liter, but I've massively cut down on my coffee drinking for some reason since I switched.
4. Up your oral hygiene regimen. While having a particularly bad case of VT, I had to brush my teeth four times a day. I actually brought my brush and paste with me to work!
Finally while this is not necessarily VT related, I would suggest finding several new vapes you like a lot too. For some reason if I vape the same juice a lot I get to where I can't really taste it--like it is nothing but background noise or something--without having device problems or vaper's tongue.
I find that variety keeps my tongue happy.
ETA: Also it could be smoking cessation related. It took me about a week from quitting smoking to lose all sense of taste, and a month for it to come back. Also, I don't know if this is true for everyone, but if I'm having sinus problems like say I have a cold or my allergies are being particularly bad (seasonal allergies) I can't taste my juice or well anything else either. I'm no doctor but I think that the sense of taste is linked to the sense of smell.
