This is what I found about withdrawal bleeding...
Breakthrough bleeding (BTB) or spotting is the occasional, irregular bleeding/spotting you may experience while using a hormonal method of birth control. BTB is most common when you first start using a method (or when you switch brands, or regimens) and it usually stops after the first 2-6 months of use. Whether you experience BTB will depend on the brand, the method, and your body. [It depends on how fast or how slow your body metabolizes hormones, in particular estrogen.] Moreover, BTB can occur whether you're using birth control to prevent a pregnancy or to manage your period.
Like the fake period (withdrawal bleeding), BTB has nothing to do with your menstrual period. BTB is caused by the amount of hormones in birth control. Think of BTB as an "adjustment"--the bleeding/spotting occurs because the body is adjusting to the hormone dosages in the birth control method. [Of course, the BTB pattern will depend on the particular method you're using--e.g., expect a fair amount with some of the progestin-only methods.]
I actually don't think some doctors know what they're talking about. I know they are 'general practitioners' so they should know a little about a lot but if they're contradicting each other I don't know where that leaves us!
