One of the best supplements I have taken for the liver is Milk Thistle Plus, by Rainbow Light.
Every six weeks is fine. I have done them every 2 weeks when feeling awful. They recommend every 2 to 4 weeks (I think 4 is prob better).
But flushes alone might not be enough to decongest your liver, as I am currently struggling with similar issues. colonic irrigation helps to detox, and acupuncture is helping too (finding the right practitioner really makes a difference).
You can also check out the herbs@SensibleHealth (dot com) I just got them and took the Copsis last night for first time. Seemed to have a real positive effect, and helped me to sleep better. I ordered the 4 pack they sell of all the liver/gallbladder herb tinctures.
Hang in there! You're among friends and fellow sufferers :)