Actually, instead of increasing the nicotine strength of your
e-liquid, you may want to consider boosting the intensity of your vape by increasing the power (measured in watts) of your device. This certainly will help if it is the TH that is lacking for you.
You didn't mention what setup you are using. For the purpose of this post, I'll assume that it is some type of 650+ mAh fat batt (e.g., eGo, Riva, KGO, Go-Go, iGo, etc.). With the same 3.2-3.7V battery, using an
LR (low resistance) atomizer or cartomizer will provide much more kick (and more vapor). This is the simplest and least expensive way to increase power. It does, however, put strain on your fat batt's
mosfet. ['mosfet': a cute little mouse-like creature living in your fat batt's switch. It is allergic to the high amps (gremlin) associated with LR attys and cartos.]*
* FYI: There also is this boring technical definition of 'mosfet': metaloxidesemiconductor field-effect transistor used for amplifying or switching electronic signals. Also, there are those who claim that 'amps' are not gremlin, but a measure of electrical current. All agree that too many amps are unhealthy for mosfet.
A safer, but more expensive way to increase power is by moving up to a high or variable voltage
mod.
This page of
The Wonderful World of Mods describes such devices and mentions most of those that were available last year. Newer VV mods include the ProVari, Infinity, and Darwin (which, more accurately, is regulated power).
For more information on this volts/ohms/watts stuff, see this page of the
Wonderful World of Vaping V2. More info on LR attys/cartos and amps can be found
here.