MD Diet of Temecula Medical Weight Loss and Medical Spa

There is no evidence to my knowledge that doing more filler will help it to last longer.  Filler does not last longer the second or third time you do it, but if you are consistently getting injected every couple months the amount of product in your lips will continue to build.  I find that Juvederm in the lips typically lasts 6-9 months.  

Over time the filler will metabolize and you will go back to your original appearance.  There is some thought that filler will stimulate collagen production and leave you in a better place than you started.  I usually recommend coming is for a touch up ever 6 months to a year.   

From your photos it appears that the placement of the Juvederm was above your natural lip line causing a shelf appearance.  I would recommend dissolving all of the product and starting over with a new injector.