Extremely heavy intermenstrual bleeding despite taking the pill?

Hey… I've been taking the pill for 11 weeks now, on the recommendation of my gynecologist (it's also the first time I've taken it).

I'm currently taking a one-week break from the pill because I've been experiencing very light spotting for the past two weeks. It was always very old, dark blood in very small amounts—more like drops.

Today is day 5 of not taking the pill, and I've been bleeding very, very heavily for four days now. I've never had a period this heavy, for example. I'm also having pretty severe cramps.

Is this cause for concern?

Thanks for your help!