Bleeding between periods?? on the pill?

Been on Low-Ogesterol for about 3 years now. Last year I was told it was ok by my Dr. to "double-up" on packs and instead of taking the pill for 3 weeks, then a week off to get my period, that week off I would just immed. start a new pack and not get my period until the end of the pack (aka: 6 weeks without a period), so I tried it a few times and had NO problems. Well I started a new pack on the 19th (when I was supposed to have my period) and everything was fine, until today, I have some dark brown blood, it's not heavy, but it just started today. Going to call the Dr. in the morning, just curious if I should continue the rest of the pack (the pills end on Nov. 8 so like 10 days) and then leave it for a week and then start another pack? Will this breakthrough bleeding last long? Obviously after this I will not be "doubling up" on packs. Thanks