Filler duaration is affected by many factors: area, filler used (brand, technology, rheology), deph of injection, tecnique and instrinsic factors. There are many factors that can stimulate a greater rate of degradation of HA fillers, and that includes your own matebolism and other factors such as excersise. As you may know already, it also depends on the brand and reticulation of HA, viscosity and area where is injected. The facial mimic and mobility of the area, such as in the lips, also contributes to reduce the duration of the fillers. Now, I have seen cases of lower than expected duration, and in some cases, patients are to increase filler duration in the area after subsequent sessions. But I haven't seen in my practice such high rate of degradation. But even in such a case, I must point out that 8 ml in 3 months period, is too much. I usually treat with 1 ml a month, that will give time for remodeling of the area and swelling to completely dissapear an tissues to heal and adapt.
Tecta is not the cause (is antacid, a medication to reduce the prodcution of Hydrochloric acid in the stomach, it does not affect HA).
I would suggest, after checking your medical history thorougly, to consider a change of brand and therefore, technology of HA, such as Restylane (NASHA are not my favorite for this area, but I would consider as you have used Define before), Belotero, Aliaxin or Theosyal. Calcium based fillers (such as Radiesse) are not indicated for the lips, as it produces bumps and irregularities.