First... what coil is it? (metal)
Second, you cannot "clean" a cartridge coil. You might get some of the crap in the center off, but the coil itself and the ceramic can't be cleaned.... I tried a bunch of techniques that wouldn't damage the ceramic and none worked.
Third, nicotine would not make a liquid "burn" differently. It doesn't work that way, if it's harsher, then you're sensitive to the level used.
Forth, you should never dry burn a cartridge, regardless if it's ceramic, if anything, you're damaging the ceramic and could end up fracturing it and inhaling the dust.
Five, ceramic is a porous material, which with liquids with sweeteners, will clog up, and can do this very fast depending on the liquid.
Are you in wattage mode or is it one of the TC coils?
Those coils can last up to a month but can also be clogged up within a few days depending on the liquid used and how it's used (wattage or TC).
I've use a lot of Vaperasso's cCell coils so I know them quite well, I even made a thread that I show how to rebuild them. (check my blog if interested).