You won't get the full effects until week six and ideally, your doctor would run your labs then and adjust your dose accordingly. But, twelve weeks isn't unreasonable.
After six weeks at 100mg, my doc ran blood tests and bumped me to 130mg, and after another twelve, bumped me to 140mg, which is where I am almost two years later. I began to feel the effects at about six weeks and they just kept getting better for the first six months or so. It takes a while to get fully up to speed, so be patient.