Hi Qtpuff. Welcome to the ECF. Congratulations on the upgrade.
What device had you used prior to the volcano? What strength where the refills?
As far as the headaches ,you may have too high nicotine content in your new liquid. Or you may be overly sensitive to one of the componants in your liquid. Volcano lists that it is a PG/VG blend but they dont list what percentage. I would say try a diferent liquid, one that is known to be 100%VG and one that is also 100%PG .While you are buying liquid get a mix less than your current 24mg...say 18?.. On a secondary note do you know that when you vape you should increase your water intake? Vaping dehydrates us and one of the first signs of dehydration is headache..... One of these will likely be your culprit this is the only thing I can think of that would cause a headache.
Yes you can drip down the side wall of the carto into the cartomizer but if the tank is working correctly you shouldnt need to. You wont be able to fill the tank that way but if you get in a spot where you cant disassemble the tank and fill it that would get you a good vape with very little chance of burning your carto. Did the instructions included with the tank tell you to fill the carto before inserting it into the tank, then fill the tank? Thats how I was told to fill my carto tank and I must say that is the only way it works correctly. Good Luck. Happy Vaping.