You probably are stressing the pod. 3mg/ml is a very low nicotine level for someone just quitting smoking. It would probably be ok in a sub-ohm system, where you get more nicotine per hit because it's direct to lung. Most people when they quit use 18-24mg/ml at first. You've been off the cigarettes for the most part for a while and weren't that heavy of a smoker. You might consider trying 12mg/ml for a while, then tapering down to 6 then 3. It would probably help get you off those last few cigarettes that you have to have as well. The other option is switching to a sub-ohm system. It all depends on whether you prefer mouth to lung of the pod or direct lung of the tank. You should look into getting another system anyway and have the caliburn as a backup. Every vaper should have backups to their favorite mod in case of loss or breakdown.
ETA: I don't think the PG/VG ratio is a big enough factor that you should change it if you have issues with the PG.
ETA: I don't think the PG/VG ratio is a big enough factor that you should change it if you have issues with the PG.