What Causes Mild Hot Flashes Despite Taking Oestradiol Post Hysterectomy?

I had a total hysterectomy 2 years ago. I am 51 and have been taking Estridial 1mg daily. I eat flax seed, take multivitamins, eat organic as much as possible, I exercise 20-30 minutes 4-5 times per week, but still have mild hot flashes. I would like to find a natural hormone replacement or simply go off the perscription. I have heard that I have to take estrogen for the rest of my life.