As a heating coil is used over time, the resistance (ohm rating) will often raise. This is due to e-liquid buildup of gunk on the coils from the sweeteners used. Some coils allow "dry burning" this gunk off the wire to prolong the continued use of the coil, but with many clearomizers the best thing to do is to simply replace the coil head.
This may at first appear to be an expensive solution, however compare the cost of replacement coils every week or so, to what you paid for cigarettes for the same time period...and you'll see that you making out good financially with vaping over smoking.
Consider upgrading you juice delivery device to one which allows homemade coils (rebuildable drip atomizers, Kayfun-style RDA's, etc),
Information Resources for Your First RBA. Being able to dry burn homemade coils can extend their life for months at a time and is much cheaper in the long run. The homemade coils in my drip atomizer (Patriot) are over 3 months old; I simply dry burn the coils with each wick change (every 3 - 4 days).
