your period comes from a drop in progesterone - if you took two pills at once, your p4 would have gone higher, and when you returned to the lower level, it would think it was a drop and is trying to have a bleed (but isn't fully bleeding because you still have P4 from the pill that you're on -just at the lower level than you had when you doubled up)

geez, i know what i'm trying to say - just not sure i'm saying it well - does that make sense hun?